Measurement of non-VKA oral anticoagulants versus classic ones: the appropriate use of hemostasis assays
Thrombosis Journal volume 12, Article number: 24 (2014)
Traditional anticoagulant agents such as vitamin K antagonists (VKAs), unfractionated heparin (UFH), low molecular weight heparins (LMWHs) and fondaparinux have been widely used in the prevention and treatment of thromboembolic diseases. However, these agents are associated with limitations, such as the need for regular coagulation monitoring (VKAs and UFH) or a parenteral route of administration (UFH, LMWHs and fondaparinux).
Several non-VKA oral anticoagulants (NOACs) are now widely used in the prevention and treatment of thromboembolic diseases and in stroke prevention in non-valvular atrial fibrillation. Unlike VKAs, NOACs exhibit predictable pharmacokinetics and pharmacodynamics. They are therefore usually given at fixed doses without routine coagulation monitoring. However, in certain patient populations or special clinical circumstances, measurement of drug exposure may be useful, such as in suspected overdose, in patients experiencing a hemorrhagic or thromboembolic event during the treatment’s period, in those with acute renal failure, in patients who require urgent surgery or in case of an invasive procedure. This article aims at providing guidance on laboratory testing of classic anticoagulants and NOACs.
Anticoagulants are a mainstay of cardiovascular therapy and, until recently, vitamin K antagonists (VKAs) were the only oral anticoagulants available. The knowledge about monitoring and dosing of VKAs in order to maximize their efficacy and minimize hemorrhagic complications has increased considerably since their introduction in 1950s. In addition, the management of VKAs has been optimized with the establishment of anticoagulation clinics, as well as self-monitoring and self-management programs. However, VKAs have still strong limitations such as a slow onset and offset of action, the requirement of variable dose regimen, a series of multiple drug-drug interactions and a considerable inter-individual variability. These limitations make coagulation monitoring and frequent dose adjustments necessary to ensure an adequate level of anticoagulation. Unfractionated heparin (UFH) and low molecular weight heparins (LMWHs) are also a cornerstone in the armamentarium of anticoagulation. While UFH has to be monitored closely due to unspecified bindings to proteins, endothelial cells and macrophages conducing to a variable response from patient to patient, the interest of monitoring LMWHs is controversial but suggested in specific situations such as in extreme body weights, severe renal insufficiency, pregnancy and cirrhosis.
Non-VKA oral anticoagulants (NOACs) have major pharmacologic advantages over VKAs, including a rapid onset/offset of action, fewer drug interactions, and predictable pharmacokinetics, eliminating theoretically the requirement of regular coagulation monitoring. Regulatory agencies have approved NOACs for various indications based on the results of large phase-III clinical trials demonstrating the efficacy and safety of these compounds. Effectively, they were found at least as efficacious, if not better, than warfarin in the setting of stroke prevention in adult patients with non-valvular atrial fibrillation (NVAF) [1–4] and in the treatment and the secondary prevention of venous thromboembolism [5–9]. Compared to LMWHs, these agents also proved their non-inferiority or superiority for initial treatment of venous thromboembolism and for thromboprophylaxis in patients undergoing hip or knee arthroplasty, [10–20]. Non-VKA oral anticoagulants will certainly replace some of the traditional anticoagulants in the future but it is important to keep in mind that the introduction of these new agents will also change the strategies of patient management and of the hospital routine . Therefore, the knowing of the pharmacology and the impact of these new compounds on routinely used coagulation assays is of great importance to achieve optimal patient outcomes. Moreover, it is anticipated that a non-negligible proportion of patients will reach either insufficient or supra-therapeutic level when given at fixed dose leading to the introduction of dedicated coagulation tests that respond faithfully to the pharmacodynamics of NOACs.
The aim of this review is to define why, when and how to measure traditional anticoagulant and NOACs.
Pre-treatment biological screening
The following information should be collected before prescribing an anticoagulant at therapeutic or prophylactic dose: cell blood count, prothrombin time (PT), activated partial thromboplastin time (aPTT) and renal function.
In clinical trials of oral anticoagulants, drug eligibility and dosing were determined using the Cockcroft-Gault equation to estimate creatinine clearance (CRCL) as a measure of renal function. Importantly, it was proved that the use of modification of diet in renal disease (MDRD)-derived estimated glomerular filtration rate (eGFR) instead of Cockcroft-Gault in prescribing anticoagulants leads to overestimation of renal function in lower values [24–26]. Thus, many elderly patients would either incorrectly become eligible for them or would receive a too high a dose.
Samples acquisition, processing and storage
Sample acquisition and processing are of great importance since it was proven that each component of the specimen collection system (needle gauge, composition of the collecting tube, concentration of sodium citrate) may potentially impact the results for coagulation testing . This should be performed according to international recommendations .
For example, contamination of the citrate solution by divalent ion such as magnesium influences PT .
For UFH and LMWH monitoring, there is a risk of platelet activation between sampling and centrifugation that leads to neutralization of heparin by binding to PF4 and underestimation of anti-Xa activity. If sampling is performed in citrated tubes, it is important that the delay between sampling and centrifugation is lower than 1 hour and thus to warn the laboratory before sampling. The sample should also be tested within 4 hours  The sample may also be collected in a mixture of citrate 109 mM, theophylline, adenosine and dipyridamole (CTAD) which allows increasing the acceptable delay between sampling and centrifugation to 4 hours [30, 31]. Heparin is lost more rapidly in citrate tubes that contain a large air space (after addition of blood) due to accelerated platelet activation and release of PF4. This effect is suppressed if CTAD is used .
Biological monitoring of anticoagulant treatments
Vitamin K antagonists
Vitamin K antagonists produce their anticoagulant effect by interfering with the cyclic regeneration of vitamin K from the oxidized form to the reduced form. This is achieved by inhibiting the vitamin K epoxyde-reductase. Reduced vitamin K is necessary for the γ-carboxylation of glutamate residues of factors II, VII, IX, X, protein C, S and Z. These compounds are also known for their highly unpredictable pharmacokinetics and pharmacodynamics from patient to patient, their narrow therapeutic range, as well as for their numerous interactions with food and drugs [33, 34]. There is hence a real need for monitoring those treatments in order to ensure their efficacy and to minimize hemorrhagic complications.
The PT has been widely used to monitor patients under VKA. It is based on adding thromboplastin, a substitute of endogenous tissue factor (TF), and calcium to citrated decalcified platelet poor plasma (PPP), in order to generate fibrin clot formation . Various factors are to be considered when interpreting results of PT, such as the composition of thromboplastin and the coagulometer (optical or mechanical detection) used for its determination. Thromboplastin reagents are usually made of TF, phospholipids, calcium, and often contain an inhibitor of heparin such as polybrene. The two most common sources of TF are rabbit brain and human recombinant preparations. Lupus anticoagulant or hematocrit may also influence the PT. When introducing a novel thromboplastin reagent made of relipidated tissue factor, responsiveness to lupus anticoagulants should be tested prior to monitor patients under VKA with this reagent.
Before 1980, clotting time was usually expressed in seconds or as a ratio compared to a reference value. This way of expressing results didn’t enable to compare results obtained from different laboratories or determined with different reagents or coagulometers. In 1983, the World Health Organization (WHO) developed the International Normalized Ratio (INR) to standardize the expression of PT for patients under VKA. This way of expressing PT is based on determining the International Sensitivity Index (ISI) of the laboratory thromboplastin compared to an International Reference Preparation (IRP) for which the responsiveness to VKA is known. Depending on the origin of the tissue factor, various IRP are available such as WHO human IRP rTF/95 or ECAA (European Concerted Action on Anticoagulation) rabbit reference reagent EUTHR-1 . Previously, TF was extracted from tissues such as rabbit brain or bovine extracts but nowadays, recombinant human thromboplastins with international sensitivity index (ISI) close to 1 have been designed and are replacing progressively animal reagents.
Because of the numerous variables to be considered when determining INR, each laboratory should determine its own ISI locally. However, this procedure of local determination of ISI is quite labor intensive and time consuming. It requires 60 patients stable under VKA and 20 healthy subjects. The reference technique is a manual one. The ISI determination consists of comparing PT determined with IRP on manual technique to PT determined by local coagulometer. Mean normal prothrombin time (MNPT) corresponds to the geometric mean of the 20 healthy subjects. Because of the difficulty of the procedure (e.g. the need for large numbers of normal and patients’ blood samples and the availability of reference thromboplastins), ISI calibration is now rarely performed at local hospital levels. Therefore, commercial calibrators with certified INR have been released by manufacturers in order to simplify the procedure and to validate the local ISI. However, manufacturers’ ISIs and INRs may not reflect local values as, for example, coagulometer calibration ISIs are required and INRs often vary between coagulometers even of the same model and manufacturer used in the same laboratory . Results with VKAs are expected to be further improved by two recent European Action on Anticoagulation (EAA) developments in routine oral anticoagulant control (i.e. simplified local INR derivation with the PT/INR line and prediction of further clinical events by a type of variance growth rate analysis), as demonstrated by a recent EAA multicenter study . In the PT/INR Line method, local PT is plotted against 5 certified INR for plasma calibrators and ISI is then determined using the orthogonal regression . Calibrators used for this determination may be of two different types: lyophilized or frozen plasma prepared from native patient plasmas or plasmas prepared by artificial depletion (selective adsorption) of vitamin K dependent clotting factors. Those two types of calibrators aren’t commutable due to different results . The European Society of Cardiology (ESC) Task Force on Anticoagulants has recently stated that PT/INR Line achieves reliable INR without the need for local ISI calibrations and thus recommended it. The EAA PT/INR Line test plasmas are now available in a five-plasma kit .
Recently, a variable growth rate (VGR) analysis was shown in a EAA report published in 2013 to be of greater value than the previously accepted ‘time in INR range’, in predicting ‘clinical events’ during warfarin treatment, particularly in short term oral anticoagulant .
Point of care devices
Point of care testing (POCT) has been developed for whole-blood samples in order to permit monitoring in an easier way, less invasive and more convenient for the patient. POCT devices are submitted to the same level of requirement for calibration and control as traditional determination on citrated blood . Practically, accuracy and precision of point of care testing seem to be sufficient and comparable to results obtained in a laboratory setting . Recent study revealed that point-of-care patient self-testing at home achieves high-quality warfarin therapy outside of clinical trials and compares favorably with the results achieved in randomized trials or in anticoagulation clinic settings . A recent meta-analysis show that time in therapeutic range (TTR) increased by 5% for personal self-testing (PST)/ personal self-monitoring (PSM) compared with usual laboratory-based monitoring . In addition, a significant reduction in the rate of thromboembolic complications with PST/PSM was observed but not in the rate of major bleeding or overall mortality compared with usual laboratory-based INR monitoring. The frequency of INR testing with PST/PSM is higher than usual laboratory-based monitoring , leading to less cost-effectiveness . Based on the preceding considerations, the 9th Edition of the American College of Chest Physicians (ACCP) on the Antithrombotic Therapy and Prevention of Thrombosis, makes a weak recommendation in favor of PSM (not PST) for patients treated with VKAs who are motivated and can demonstrate competency in self-management strategies, including the POC equipment .
Frequency of testing
At the start of treatment, several days or weeks may be needed to reach steady state due to particularly long VKA’s onset of action . During this stabilization period, frequent monitoring is recommended to adjust dosing based on INR determination according to validated VKA dosing normograms  computer-assisted oral anticoagulant dosage program . In patients beginning VKA therapy, INR monitoring should be started after the initial two or three doses of oral anticoagulation therapy . In the hospital setting, INR monitoring should be performed daily until the therapeutic range has been reached for at least two consecutive days . In outstanding patients, starting their treatment, monitoring may be reduced to once every few days until the patient is stabilized at the therapeutic range . For patients who are receiving a stable dose of oral anticoagulants, previous recommendations mention that monitoring should be performed at an interval of no longer than every 4 weeks (Grade 2C) . More recent recommendations advice intervals between controls may be extended to 12 weeks for patients with optimal adherence to treatment [52–55]. Patients more likely to maintain stable anticoagulation are older (>70 years), have an INR target of 2-3 (versus higher targets), and do not have heart failure . If adjustments to the dose are required, then the cycle of more frequent monitoring should be repeated until a stable dose response can again be achieved .
Prompt repeat testing after out-of range INR value is associated with better anticoagulation control (higher TTR) and could be an important part of a quality improvement effort for oral anticoagulation . The optimal recall interval after a high (>4.0) or low (<1.5) INR value is within 7 days, and within 14 days after a mildly high (3.1 to 3.9) or mildly low (1.6 to 1.9) INR value . The 9th ACCP guidelines suggest for patients taking warfarin with previously stable therapeutic INRs presenting with a single out-of-range INR within 0.5 units of the range to continue the current dose and retest the INR within 1 or 2 weeks (Grade 2C) . This suggestion is based on the concept that for patients with previously stable INR control, the single mildly out-of-range INR likely represents random variation and does not warrant a change in VKA dose; too frequent VKA dose adjustments tend to destabilize the INR leading to suboptimal control . Available evidence supports this recommendation for patients presenting with an out of range INR where there is no identifiable change in diet or medications to explain the result. However, this recommendation should not take the place of a thorough patient interview and individualized assessment of the patients risk for bleeding and thromboembolism. A one-time dose adjustment is reasonable in the setting of a temporary, but not ongoing, precipitating factor for an out of range INR. A change in maintenance dose is advisable if a precipitating factor is identified and will continue long term (e.g. a new chronic medication or dietary habit) .
Recent studies found that different factors are associate with an INR-stability in long-term management such as age <70 years, the absence of chronic diseases, and male gender while congestive heart failure, diabetes, and a target range for INR ≥3.0 were associated with instability [57, 58]. Therefore, in order to improve TTR, and thereby improve patient outcomes, it is recommended to target the INR of 2.5 and to avoid the explicit or implicit pursuit of non-standard INR targets . However, as discussed above, a VGR analysis was shown to be of greater value than the TTR in predicting clinical events [38, 41].
Dietary consumption of vitamin K is also a factor that influences the stability of the INR in patients treated by VKA. Several studies had been performed to assess to benefit of the supplementation in vitamin K in unstable patients and it seems that vitamin K supplement improved the stability of anticoagulant therapy [60–68]. Finally, for patients with INR 4.5 to 10.0 and no symptoms of bleeding, it’s recommended to skip 1 to 3 doses of VKA and retest INR. For patients with INR >10.0, give 2.5 mg oral vitamin K and retest INR next day .
Several therapeutic ranges have been proposed to assess the therapeutic effects of VKA depending on the clinical indications . There is a significant increase in bleeding risk for INR over 4.5 and thrombotic complications should be considered for INR lower than 2.0 [28, 69, 70]. In clinical studies, one should pay attention to the reliability of the INR determination. For example, in the pivotal trials comparing NOACs with warfarin, evidence of the validation of the stated INR was not provided. In RE-LY two important assessments of INR control (i.e. local ISI calibration and external quality control of INR) were not reported. This “claimed INR” makes cross-trial comparisons difficult [28, 71]. In addition, Poller et al. hypothesized that this may be one of the reasons explaining why the EAA patients receiving warfarin suffered considerably less thrombotic and bleeding episodes .
The anticoagulant response of treatment doses of heparin is highly variable  due to competition of a variable number of plasma proteins with AT for heparin binding and complex kinetics of heparin clearance. Thus, the peak activity and duration of effect increase disproportionately with increasing therapeutic doses (apparent half-life: 30 to 150 min) . Thus, UFH therapy is monitored and the dose is adjusted based on assay results. However, some studies have indicated that monitoring of therapeutic UFH in the treatment of VTE may not always be needed. Unmonitored, weight-adjusted subcutaneous heparin was found to be as safe and effective as weight-adjusted LMWH in a randomized trial of patients with VTE, suggesting that aPTT monitoring of subcutaneous heparin may not be needed . The 9th edition of the ACCP guidelines suggests that, for outpatients with VTE treated with subcutaneous UFH, weight-adjusted dosing should be used without monitoring rather than fixed or weight adjusted dosing with monitoring . In addition, a recent retrospective study has shown that routine monitoring and heparin dose adjustment may be unnecessary for patients receiving doses of at least 30 000 units/day , as for these patients, the mean proportion of time with an aPTT of 0.2 anti-Xa IU/mL was 92%. The monitoring is also performed to prevent bleeding but its utility is still controversial .
Global coagulation tests
Activated partial thromboplastin time
The most common assay used to monitor heparin is the aPTT. Based one prospective study performed in 1972 , an aPTT ratio (reported therapeutic aPTT range divided by the control value for the reagent) of 1.5 to 2.5 was adopted as the therapeutic range for UFH. However, the definition of the control value is not well established. The ACCP recommends against the use of a fixed aPTT target in seconds for any therapeutic indication of UFH [73, 78, 79]. Each laboratory should determine this reference aPTT ratio range for each combination instrument/reagent and for each lot of their cephalin. A French study has recently shown a 3 to 8 fold aPTT increase for an anti-Xa activity of 0.7 IU/mL (Table 1) . Too sensitive reagents do not allow a precise chronometric measurement and therefore should not be used for UFH monitoring [81, 82]. In addition, mechanical end point coagulometers showed greater sensitivity than optical ones .
Similar reagent/instrument combinations showed less variation in aPTT results than unlike combinations . Using the same instrument model and same reagent lot but performed in different laboratories, significant statistical and clinical differences in the heparin therapeutic range values are found, owing to variation in the individual plasma samples as well as pre-analytical and analytical variables that can vary greatly between hospitals. It is thus unacceptable for a large hospital network to determine the therapeutic range of heparins at only one institution for the whole network . In addition, the procedure of definition of therapeutic range is not defined and debated [85–87]. In the study that established the therapeutic range using the aPTT ratio, the range of aPTT ratios of 1.5-2.5 corresponds to a heparin’s level of 0.3-0.7 IU/mL as determined by anti-Xa assay . Thus, the more accurate method to determine the aPTT ratios equivalent to 0.3-0.7 is to measure aPTT ratio and anti-Xa activity of patient plasmas treated with different levels of anti-Xa. Spiking a normal pool plasma with heparin solutions at different concentrations doesn’t take the in vivo heparin metabolism into account and leads to a more prolonged aPTT in comparison to those of treated patients. The regression relationship is then used to derive the range of aPTT ratios equivalent to 0.3 to 0.7 IU/mL anti-Xa. However, this calibration method may not enhance inter-laboratory agreement in UFH monitoring  and it should be noted that the evidence linking these plasma heparin levels to the occurrence of bleeding or thrombosis is of low quality .
Activated clotting time (ACT)
Activated clotting time is used to monitor higher doses of UFH given to patients undergoing percutaneous coronary intervention (PCI) or cardiopulmonary bypass surgery, because at such higher doses the aPTT becomes prolonged to the point of becoming unmeasurable and unreliable. However, PCI and cardiopulmonary bypass surgery induce major hemostatic abnormalities [90–102]. The target ACT was determined by historical papers in 1955 and 1978 [103, 104]. The clinical relevance of this target ACT is doubtful because it has never been validated in prospective studies and because ACT reagents and instruments have changed over years. The ideal management of oral anticoagulation during cardiopulmonary bypass [105, 106] and catheter ablation for AF [107–109] is still controversial with a wide range of procedures available. During AF ablation, it’s now recommended to achieve and maintain an ACT of 300 to 400 seconds in order to reduce the risk of systemic thromboembolism . However, the ACT is affected by a lot of pre-analytical  and analytical variables [112, 113]. Finally, target ACT should be re-determined for the peri-procedural use of NOACs for AF ablation. The management of anticoagulation in adults and older children cannot be extrapolated to neonates, due to physiological differences in hemostasis and the dilutional effects of cardiopulmonary bypass in infants .
Specific coagulation tests
Chromogenic anti-Xa assays
Monitoring of UFH may also be performed by anti-Xa activity measurement. The UFH anti-Xa assay is based on the ability of heparin to accelerate inhibition of a standard concentration of FXa in the presence of antithrombin (AT). The test is performed by diluting plasma in buffer, which may or may not contain exogenous AT or dextran sulfate, and incubating with a specific concentration of FXa. Assays that add exogenous AT or dextran sulphate may overestimate the actual in vivo activity of UFH, LMWH or fondaparinux in patients with excess plasma proteins or deficient levels of AT [85, 115]. The phenomenon is also encountered in neonates since antithrombin function is significantly decreased in neonates, and by supplementing the assay with exogenous antithrombin there is a direct disturbance of the physiological scenario . The advantage of anti-Xa activity over aPTT is to not be influenced by variation of inflammatory proteins like factor VIII or fibrinogen, by factor deficiencies and lupus anticoagulant. The anti-Xa activity is also preferred to aPTT in children less than 1-year-old , in case of prolonged aPTT before treatment initiation and for patients with important inflammatory syndrome affecting aPTT . When the baseline prolongation of aPTT is due to lupus anticoagulant, an insensitive reagent (giving a normal baseline aPTT) should be used . Qualitative or quantitative AT deficiency should evoke a biological or clinical heparin resistance, with an abnormally short aPTT and a weak anti-Xa activity (when measured by a method without in vitro addition of antithrombin). There are differences between commercially available methods but the clinical relevance seems to be limited .
Finally, a recent large retrospective cohort analysis has shown that patients with disproportionate prolongation of aPTT relative to anti-Xa activity did have a highest 30-day mortality and a highest risk of bleeding. If these data are confirmed prospectively, it may be useful to measure both aPTT and anti-Xa .
Low molecular weight heparins
Low molecular weight heparins show a more predictable anticoagulant response than UFH because the shorter heparin chains exhibit lowered affinity for heparin binding proteins in the plasma. Moreover, thanks to reduced binding to the endothelium, LMWHs have a longer half-life than UFH, and the half-life is dose-independent. LMWHs with longer chain lengths have shorter half-lives than LMWHs with shorter chain length, and therefore are less prone to accumulation. LMWHs are cleared by the kidneys and therefore, can accumulate in the plasma of patients with impaired renal function. Typically, LMWHs are given in fixed- or weight-adjusted doses without monitoring. ACCP guidelines recommend against routine coagulation monitoring (grade 1C) . Indeed, data on the correlation between anti-Xa levels and bleeding risk are controversial . A randomized controlled trial comparing monitored versus unmonitored dalteparin therapy for the treatment of VTE showed no benefit of monitoring . In addition, routine monitoring of anti-Xa levels is costly and inconvenient for physicians, patients and laboratory.
LMWHs may produce some prolongation of the aPTT (from 0.6 IU/mL of LMWH ), but their effect on the aPTT is less than that of UFH. Thus, aPTT cannot be used for monitoring . Therefore and accordingly, the measurement of the anti-Xa activity is the recommended test . Recommendations advice to monitor the intensity of anticoagulation via the measurement of peak anti-Xa activity levels with various target ranges depending on the LMWH preparation and the frequency of dosing (Table 1) [78, 120]. One limitation is that thresholds have not always been validated in terms of clinical outcomes .
Since every LMWH is different, LMWHs monitoring requires calibration towards the specific LMWH used for therapy . Other limitations of anti-Xa activity measurement include a poor comparability between commercially available anti-Xa chromogenic assays [121, 122], substantial inter-laboratory variation in results  and poor correlation to antithrombotic efficacy . In contrast to what is generally assumed, the inter-individual variation of the in vitro pharmacodynamics response is equally higher for UFH and any LMWH, (i.e. 25%) when measured by a global assay like thrombin generation assay [124, 125].
Thus, monitoring may be used in obese patients, in those with renal insufficiency or with cirrhosis , when therapeutic doses of LMWH are required during pregnancy and in neonates and infants .
The anti-Xa assay cannot be used in patients with liver disease to monitor AT-dependent anticoagulant drugs as it underestimated drug levels [126–129]. This underestimation is due to the acquired AT deficiency in these patients . The addition of exogenous AT corrects the drug level. Dose escalations suggested by a low anti-Xa level will potentially lead to a substantial bleeding risk . Clinical trials on the monitoring, efficacy and safety of heparins are urgently required to improve antithrombotic therapy in patients with cirrhosis.
The usefulness to monitor the intensity of therapeutic anticoagulant with LMWH during pregnancy is still controversial. Recommendations vary significantly among recent guidelines [131–134]. For a given dose of LMWH, anti-Xa levels are lower in pregnancy than in the non-pregnant state. Lower levels of anti-Xa levels in pregnant patients receiving therapeutic doses of tinzaparin are observed later in gestation [135, 136]. These observations suggest that higher doses or more frequent dosing may be required to achieve a desired anticoagulant effect among pregnant women. A recent single centre prospective case series of pregnant women requiring anticoagulation (tinzaparin at a daily dose of 175 IU/kg) therapy during pregnancy has shown that weight based anticoagulant therapy did not achieve the target range of anticoagulation throughout pregnancy with more than 50% patients showing subtherapeutic levels. Thus it does not seem that adjusting doses for increasing pregnancy weight is sufficient . Further studies in this field in urgently are required.
Obesity is an important risk factor for venous thromboembolism . Standard fixed doses are suboptimal in obese patients [139–141]. Thus, ACCP guidelines recommend weight-based dosing in obese patients receiving LMWH prophylaxis or treatment (grade 2C) .
In a meta-analysis that included data on 921 patients with a BMI >30, there was no excess in the rate of major bleeding over that observed in non-obese patients who received LMWH in doses adjusted by total body weight . For thromboprophylaxis with fixed-dose enoxaparin and nadroparin, there is a strong negative correlation between total body weight and anti-Xa levels in obese patients [78, 139]. In contrast, prescribing approximately 0.5 mg/kg of enoxaparin daily results in anti-Xa levels that are within or near target levels . In a recent large prospective study on 3928 morbidly obese inpatients, high-dose thromboprophylaxis approximately halved the odds of symptomatic VTE, with no increased risk of bleeding . In conclusion, further studies regarding optimal doses for obese patients with anti-Xa factor measurements are still required.
Several renal insufficiency
Appropriate dosing of LMWHs in patients with renal insufficiency is less clear. There is an inverse relationship between CRCL and anti-Xa levels [78, 144, 145] and the risk of bleeding complications with LMWHs is higher in patients with impaired renal function [78, 146, 147]. Severe renal insufficiency (CRCL lower than 30 mL/min) is a contra-indication of randomized controlled trials evaluating efficacy and safety of LMWHs. In such patients, UFH is, in most cases, a better choice than LMWHs despite numerous drawbacks , as UFH is less dependent on renal function. The data on accumulation with LMWHs other than enoxaparin is limited. When used in full therapeutic doses, nadroparin and dalteparin clearance, but not tinzaparin clearance, was shown to be correlated with CrCL[148–151]. The apparent difference in tinzaparin clearance in patients with severe renal insufficiency may reflect metabolism by hepatic mechanisms, possibly due to the higher molecular weight of tinzaparin compared with other LMWHs. Two approaches are considered to optimize the use of LMWHs in the elderly: anti-Xa monitoring or empiric LMWHs dose reduction. However, it is still debated whether there is a clear benefit in anti-Xa monitoring regarding LMWHs efficacy and safety outcomes, especially in patients with renal impairment [120, 152, 153]. Alternatively, empirically reducing the dose to 50 % of the recommended dose has also been proposed by ACCP with a low grade of recommendation for enoxaparin in patients with ACS or VTE with severe renal impairment . However, the empirical reduction of the initial enoxaparin dose without systematic monitoring could lead to an anti-Xa peak level below 0.5 IU/mL, leading to an increase of the thrombotic risk . No specific recommendations have been made for other LMWH preparations given the lack of sufficient data [78, 155]. When given in prophylactic doses, LMWHs has not been shown to increase the risk of bleeding complications, irrespective of the degree of impairment of renal function .
Neonates and infants
The variability in age-related pharmacokinetic parameter estimates (clearance, volume of distribution and half-life) leads to a different pharmacodynamics profile for anticoagulants in children in comparing to adults [116, 156]. The 9th edition of the ACCP guidelines recommend that in neonates or children receiving therapeutic LMWHs either once or twice daily the drug should be monitored to a target anti-Xa of 0.5–1.0 IU/mL in a sample taken 4–6 hours or 0.5–0.8 IU/mL in a sample taken 2–6 hours after subcutaneous injection . There is a need for robust pharmacodynamics models in pediatric practice. The current recommendations regarding anticoagulant dosing or laboratory monitoring in children are simply extrapolated from adult evidence and are not based on appropriately robust levels of evidence . Therapeutic ranges are not well correlated with clinical outcomes and assays are not standardized. In 2012, a position paper from the Perinatal and paediatric haemostasis subcommittee of the scientific and standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH), recommends a step-wise approach to the generation of this evidence . A recent study has shown that enoxaparin dose titration to achieve therapeutic anti-Xa levels may be affected by assay variability. Attempts to titrate to target anti-Xa values may result in significant dose variation that may or may not benefit pediatric patient care. Neonates or children with normal renal function may be safely treated with weight-based age-appropriate standard dosing without monitoring. Therefore, these authors suggest that a prospective, multicenter, randomized clinical trial comparing the safety and efficacy of exonaparin weight-based dosing with and without anti-Xa dose titration using an anti-Xa standardized assay, is required .
Fondaparinux is cleared only by renal function. Biological monitoring is not recommended. Anti-IIa assay and aPTT are not recommended as they have only a very low sensitivity to fondaparinux [159–161]. Anti-Xa measurement should be performed with appropriate calibration allowing results expression in ng/mL. Dose tailoring is not recommended according to anti-Xa results. The target ranges (2 to 3 days after injection) are in mean 1.41 mg/mL (0.97-1.92 for 5th and 95th percentiles). The through values are in mean 0.52 mg/mL (0.24-0.95 for the 5th and 95th percentile) for a patient receiving 7.5 mg once a day . No specific data have been published in the very elderly receiving fondaparinux at curative dose . Healthy males receiving a single 2.5 mg dose of fondaparinux had an average peak steady state (3 hours) concentration of 0.39–0.5 mg/L . In patients with deep vein thrombosis or pulmonary embolism, dosing was determined by patient weight, with either 5 mg (weight <50 kg), 7.5 mg (weight 50–100 kg), or 10 mg (weight >100 kg) administered. The mean peak steady state concentrations for all three-weight classes were 1.20–1.26 mg/L [164, 165].
Non-vka oral anticoagulants
Non-VKA Oral Anticoagulants (NOACs) have been developed to counter one of the main disadvantages of VKA treatment: the requirement of regular monitoring. However, even if these treatments are given without dose adjustments, several situations or populations may require an assessment of the intensity of anticoagulation (See the “Summary of patients/situations that could require a drug tailoring” section). Moreover, a recent investigation made by the BMJ revealed that the marketing authorization holder of dabigatran etexilate, marketed under the brand name of Pradaxa® in Europe, found that if the plasma levels of the drug were measured and the dose was adjusted accordingly major bleeds could be reduced by 30-40% compared with well controlled warfarin . Similar information was also provided in a study evaluating the effect of dabigatran plasma concentrations and patient characteristics on the frequency of ischemic stroke and major bleeding in atrial fibrillation patients in the RE-LY trial . Thus, the “one dose fits all” marketing slogans behind the approval of these drugs proved to be an illusion, for at least one of these compounds. The drug companies of the other NOACs do not yet provide such information. However, the collection, analyses and distribution of similar data are of particular importance since we cannot afford to deprive us of the opportunity to improve the safety/efficacy profile of these drugs by implementing risk minimization measures, if feasible.
Summary of patients/situations that could require a drug tailoring
Even if NOACs are presented as having a predictable pharmacodynamics and pharmacokinetics, several patients or situation could require an assessment of the degree of anticoagulation and probably a drug tailoring.
The clinical situations include: recurrence of thrombosis or bleeding, before urgent surgery or procedure (with last administration in the last 24 h or more if CRCL <50mL/min), before fibrinolytic therapy of acute ischemic stroke, in case of bridging therapy, in case of cardioversion and in the setting of dual or triple antithrombotic therapy, such as in the patient with AF undergoing a percutaneous coronary intervention, when dual platelet inhibitors may be added to NOACs, given that such patients represent a complex management problem.
In addition, several patterns in patient status could also require an assessment of the responsiveness at the individual level. This includes patients with risk factors for NOACs accumulation or too low levels (i.e. drug-drug interactions as with frequently used medication like amiodarone and verapamil), patients with extreme body weight (<50 kg or >110 kg), patients with hepatic impairment, patients with renal impairment (in case of progressive decrease of renal function but also in acute decrease during dehydration, antibiotics administration, …), in case of comorbidities or in elderly patients.
How to accurately measure plasma drug concentrations?
In this part of the manuscript, we review the different routine coagulation tests that could be used to estimate the intensity of anticoagulation in patients treated with dabigatran etexilate (the pro-drug of dabigatran, a direct thrombin inhibitor) and with rivaroxaban or apixaban, two direct factor Xa inhibitors. More specific assays used to accurately estimate plasma drug concentrations are also presented.
Global coagulation tests
Dabigatran: activated Partial Thromboplastin Time
The recent recommendation of the Subcommittee of Control of Anticoagulation of the Scientific and Standardisation Committee of the ISTH, mentions that the aPTT using most available reagents can be used to determine the relative intensity of anticoagulation due to dabigatran. However, they state that aPTT should not be used to quantify the drug plasma concentration. They add that each laboratory should be aware of the sensitivity of their aPTT assays to dabigatran and this can be achieved using commercially available plasma calibrants . However, it is unknown if specific dabigatran calibrants, used out of their dedicated platform context, are truthful calibrants that could reflect accurately the impact of dabigatran in plasma from patient’s sample, since aPTT is affected by numerous pre-analytical and biological variables.
It is stated in the EU-SmPC that when dabigatran was used for the prevention of stroke in NVAF with a bid dosing regimen, an aPTT ratio greater than 2xULN (or an aPTT prolongation of about 80 seconds) at trough (10-16 h after the previous dose) reflected the 90th percentile of observations (i.e. 200 ng/mL at Ctrough) and is considered to be associated with a higher risk of bleeding . However, studies revealed that the inter-reagent variability prevents using an aPTT of about 80 seconds as reflecting plasma dabigatran concentration of 200 ng/mL  (Figure 1). Similar observations have been demonstrated for the threshold proposed in VTE prevention regarding the bleeding risk . Moreover, recent findings revealed that in addition to the inter-reagent variability, the different combinations between reagents and coagulometers increased further this variability . Therefore, laboratories should be aware about the sensitivity of their aPTT reagents towards dabigatran assessed with homemade calibrants using local normal pooled plasma spiked with dabigatran.
Thus, aPTT has limited sensitivity depending on the reagent and is not suitable for precise quantification of the anticoagulant effect for several reasons. First, the aPTT is affected by pre-analytical and biological variables [172, 173]. Secondly, a prolonged aPTT is not strongly predictive of hemorrhage and patients may experience bleeding while displaying a normal aPTT [173–175] and finally, the dose-response is not linear, precluding the possibility to differentiate minor versus major overdoses (Figure 1).
Rivaroxaban: Prothrombin Time/INR
The Subcommittee of Control of Anticoagulation of the Scientific and Standardization Committee of the ISTH mentions that PT (with a sensitive reagent) can be used to determine the relative intensity of anticoagulation in emergency situation when required, but should not be used to quantify drug plasma concentrations . However, PT results of samples from patients treated with rivaroxaban cannot be translated to INR values since INR was developed to normalize PT in patients treated by VKA thanks to the International Sensitivity Index (ISI) specifically determined for VKA therapy.
In-vitro studies reported a large PT reagents variability and, as for dabigatran and the aPTT, the different combinations between PT reagents and coagulometers increased further this variability [160, 171, 176–178] suggesting that laboratories should be aware about the sensitivity of their own reagent towards rivaroxaban (Figure 2). The Subcommittee of Control of Anticoagulation of the Scientific and Standardization Committee of the ISTH support this statement . Nevertheless, one weakness of this approach is that commercially available calibrants are labelled to be used with their corresponding chromogenic anti-Xa assays. Therefore, similarly to dabigatran and the aPTT, the quality and the accuracy of these calibrants for the calibration of PT reagents are not warranted. In addition, an ex-vivo study revealed a poor correlation between calibrated-PT and measured rivaroxaban plasma concentration .
Therefore, depending on the reagent, PT must not be used to estimate rivaroxaban concentrations in plasma and poorly reflects the intensity of anticoagulation due to rivaroxaban. The poor sensitivity, the important variability and the poor linear correlation with the LC-MS/MS in patients’ plasma samples preclude the use of PT to estimate rivaroxaban plasma concentration.
Apixaban: Prothrombin Time/INR or modified PT
As stated for rivaroxaban, INR must not be used for the assessment of apixaban while PT, either expressed in seconds or as ratio, is not sensitive enough to ensure an accurate quantitative measurement of apixaban [180–182]. Moreover, depending on the reagent, PT may be normal with therapeutic concentration of the drug [182, 183]. For the most sensitive reagents it may only inform the clinician if the patient is taking the drug. This inter-reagent variability (Figure 3) prevents valid recommendations of cut-offs in seconds associated with a bleeding risk applicable to all reagents . In addition, drugs or hematologic abnormalities affecting at least one factor assessed by PT could bias the conclusions. We definitively do not recommend PT to estimate plasma concentration of apixaban. During the early clinical development of a series of novel factor Xa inhibitors, a modified PT (mPT) assay was developed in which calcium chloride (CaCl2) was added to the thromboplastin reagent in order to prolong clotting times and, hence, increase the sensitivity of the dose–response curve for the direct factor Xa inhibitor . Thus, mPT method could be used for the assessment of the pharmacodynamics activity, but the limitations highlighted previously for PT might remain valid and the inter-reagent and inter-individual variability must be assessed. With further development and standardization, this assay could provide a potential option [181, 184].
Specific coagulation tests
Dabigatran: dilute Thrombin Time (dTT): Ecarin Clotting Time (ECT) and Ecarin Chromogenic Assay (ECA)
Thrombin Time (TT) was demonstrated to be too sensitive towards dabigatran [170, 185] and led to the development of a calibrated diluted thrombin time (dTT) using dabigatran standards to calculate the plasma concentrations. Hence, the CE-marked Hemoclot Thrombin Inhibitor® (HTI) was developed and has been proposed as a rapid, standardised and calibrated assay to determine plasma concentrations of dabigatran [170, 185–187]. The coagulation test is based on the addition of highly purified thrombin in the α-form in plasma samples pre-diluted in physiological serum (1/8 ratio) and normalized with a defined amount of normal pooled plasma. By diluting plasma samples, the test is less sensitive to dabigatran and allows the quantitation of dabigatran concentration from 50 to 500 ng/mL. It is fully automatable and has been adapted to different coagulometers in order to be easily implemented in laboratories. Several studies showed that HTI highly correlates with dabigatran plasma concentrations measured by LC-MS/MS in patient’s plasma [185, 186, 188, 189]. Nevertheless, for the accurate determination of dabigatran plasma concentrations below 50 ng/mL, the more sensitive LC-MS/MS method is still required [186, 188].
The ECT assay provides a direct measure of the activity of direct thrombin inhibitors. Ecarin is a snake venom extracted from Echis carinatus. Ecarin cleaves prothrombin to form meizothrombin, an active effector able to transform fibrinogen to fibrin. Meizothrombin is sensitive to direct thrombin inhibitors (DTIs) but is unaffected by heparin and its derivatives as well as by antithrombin . While development of commercial kits may improve the practicality of this test, these kits have not been standardised or validated with dabigatran . For these reasons, ECT cannot be recommended for emergency monitoring of anticoagulant effects. Moreover, ECT is not widely available and is known to have inter-lot variability indicating that calibration is also required with this test .
Recently, the ECA, the chromogenic variant of ECT, has been specifically developed to accurately estimate the plasma concentration of dabigatran and other DTIs in plasma. In this test, ecarin converts an excess of exogenous prothrombin added in the diluted plasma sample to form meizothrombin. The cleavage of the chromogenic substrate by the residual meizothrombin released p-nitroaniline (pNA) that can be measured at 405nm. The quantity of pNA generated is inversely proportional to the quantity of DTIs in the plasma. For dabigatran measurements, the test is calibrated with standard calibrants and provides a lower limit of quantitation similar to the one obtained with HTI. However, this test is not yet approved [188, 189, 191].
Rivaroxaban: chromogenic anti-Xa assays
Thanks to specific calibrants and controls containing a defined amount of rivaroxaban, a dedicated chromogenic anti-Xa assay has been proven to accurately estimate plasma rivaroxaban concentrations >30 ng/mL . Several chromogenic anti-Xa assays are available on the market, however, only some of them are labelled to ensure the quantitation of rivaroxaban plasma concentrations. It is therefore important to work on specific coagulation platforms where it was previously found that the mean CV is lower in the inter-laboratory setting .
However, taking into account the lower sensitivity of chromogenic assays compared to LC-MS/MS and the variability of coagulation analysers that may further increase the imprecision at the lowest concentrations, detection and quantitation of lower levels (<30 ng/mL) in rivaroxaban treated patients still requires LC-MS/MS analyses [179, 193]. Consequently, the LC-MS/MS is required for quantification of very low to moderate rivaroxaban concentrations (3 to 30 ng/mL) in clinical samples.
Apixaban: chromogenic anti-Xa assays
Due to their good sensitivity towards the inhibition of FXa by apixaban, chromogenic anti-Xa assays calibrated with specific apixaban calibrants could estimate plasma drug concentrations [181, 183]. Patients of the APPRAISE-1 study had participated in a PK/PD study suggesting that apixaban-mediated anticoagulant effect can be detected using a standard laboratory chromogenic anti-Xa assay with either LMWH or apixaban calibrants . However, the authors failed to mention that the chromogenic anti-Xa assay tended to underestimate the plasma drug concentration when comparing plasma apixaban concentrations estimated by the calibrated STA®-Rotachrom® and the true plasma concentration measured by LC-MS/MS . Thus, further studies are required with validated calibrants to compare dedicated calibrated chromogenic anti-Xa assays with LC-MS/MS in real-life patients treated by Eliquis®. As for rivaroxaban, it seems to be preferable to work on specific coagulation platforms to reduce the inter-laboratory CV [183, 195].
Connolly SJ, Ezekowitz MD, Yusuf S, Eikelboom J, Oldgren J, Parekh A, Pogue J, Reilly PA, Themeles E, Varrone J: Dabigatran versus warfarin in patients with atrial fibrillation. N Engl J Med 2009, 361: 1139-1151. 10.1056/NEJMoa0905561
Patel MR, Mahaffey KW, Garg J, Pan G, Singer DE, Hacke W, Breithardt G, Halperin JL, Hankey GJ, Piccini JP: Rivaroxaban versus warfarin in nonvalvular atrial fibrillation. N Engl J Med 2011, 365: 883-891. 10.1056/NEJMoa1009638
Granger CB, Alexander JH, McMurray JJ, Lopes RD, Hylek EM, Hanna M, Al-Khalidi HR, Ansell J, Atar D, Avezum A: Apixaban versus warfarin in patients with atrial fibrillation. N Engl J Med 2011, 365: 981-992. 10.1056/NEJMoa1107039
Giugliano RP, Ruff CT, Braunwald E, Murphy SA, Wiviott SD, Halperin JL, Waldo AL, Ezekowitz MD, Weitz JI, Spinar J: Edoxaban versus warfarin in patients with atrial fibrillation. N Engl J Med 2013, 369: 2093-2104. 10.1056/NEJMoa1310907
Investigators E, Bauersachs R, Berkowitz SD, Brenner B, Buller HR, Decousus H, Gallus AS, Lensing AW, Misselwitz F, Prins MH: Oral rivaroxaban for symptomatic venous thromboembolism. N Engl J Med 2010, 363: 2499-2510.
Investigators E-P, Buller HR, Prins MH, Lensin AW, Decousus H, Jacobson BF, Minar E, Chlumsky J, Verhamme P, Wells P: Oral rivaroxaban for the treatment of symptomatic pulmonary embolism. N Engl J Med 2012, 366: 1287-1297.
Schulman S, Kakkar AK, Goldhaber SZ, Schellong S, Eriksson H, Mismetti P, Christiansen AV, Friedman J, Le Maulf F, Peter N: Treatment of acute venous thromboembolism with dabigatran or warfarin and pooled analysis. Circulation 2014, 129: 764-772. 10.1161/CIRCULATIONAHA.113.004450
Agnelli G, Buller HR, Cohen A, Curto M, Gallus AS, Johnson M, Masiukiewicz U, Pak R, Thompson J, Raskob GE: Oral apixaban for the treatment of acute venous thromboembolism. N Engl J Med 2013, 369: 799-808. 10.1056/NEJMoa1302507
Hokusai VTEI, Buller HR, Decousus H, Grosso MA, Mercuri M, Middeldorp S, Prins MH, Raskob GE, Schellong SM, Schwocho L: Edoxaban versus warfarin for the treatment of symptomatic venous thromboembolism. N Engl J Med 2013, 369: 1406-1415.
Eriksson BI, Borris LC, Friedman RJ, Haas S, Huisman MV, Kakkar AK, Bandel TJ, Beckmann H, Muehlhofer E, Misselwitz F: Rivaroxaban versus enoxaparin for thromboprophylaxis after hip arthroplasty. N Engl J Med 2008, 358: 2765-2775. 10.1056/NEJMoa0800374
Kakkar AK, Brenner B, Dahl OE, Eriksson BI, Mouret P, Muntz J, Soglian AG, Pap ÁF, Misselwitz F, Haas S: Extended duration rivaroxaban versus short-term enoxaparin for the prevention of venous thromboembolism after total hip arthroplasty: a double-blind, randomised controlled trial. Lancet 2008, 372: 31-39. 10.1016/S0140-6736(08)60880-6
Lassen MR, Ageno W, Borris LC, Lieberman JR, Rosencher N, Bandel TJ, Misselwitz F, Turpie AG, Investigators R: Rivaroxaban versus enoxaparin for thromboprophylaxis after total knee arthroplasty. N Engl J Med 2008, 358: 2776-2786. 10.1056/NEJMoa076016
Turpie AG, Lassen MR, Davidson BL, Bauer KA, Gent M, Kwong LM, Cushner FD, Lotke PA, Berkowitz SD, Bandel TJ: Rivaroxaban versus enoxaparin for thromboprophylaxis after total knee arthroplasty (RECORD4): a randomised trial. Lancet 2009, 373: 1673-1680. 10.1016/S0140-6736(09)60734-0
Eriksson BI, Dahl OE, Rosencher N, Kurth AA, van Dijk CN, Frostick SP, Kalebo P, Christiansen AV, Hantel S, Hettiarachchi R: Oral dabigatran etexilate vs. subcutaneous enoxaparin for the prevention of venous thromboembolism after total knee replacement: the RE-MODEL randomized trial. J Thromb Haemost 2007, 5: 2178-2185. 10.1111/j.1538-7836.2007.02748.x
Eriksson BI, Dahl OE, Rosencher N, Kurth AA, van Dijk CN, Frostick SP, Prins MH, Hettiarachchi R, Hantel S, Schnee J, Büller HR: Dabigatran etexilate versus enoxaparin for prevention of venous thromboembolism after total hip replacement: a randomised, double-blind, non-inferiority trial. Lancet 2007, 370: 949-956. 10.1016/S0140-6736(07)61445-7
Committee R-MW, Ginsberg JS, Davidson BL, Comp PC, Francis CW, Friedman RJ, Huo MH, Lieberman JR, Muntz JE, Raskob GE: Oral thrombin inhibitor dabigatran etexilate vs North American enoxaparin regimen for prevention of venous thromboembolism after knee arthroplasty surgery. J Arthroplasty 2009, 24: 1-9.
Eriksson BI, Dahl OE, Huo MH, Kurth AA, Hantel S, Hermansson K, Schnee JM, Friedman RJ: Oral dabigatran versus enoxaparin for thromboprophylaxis after primary total hip arthroplasty (RE-NOVATE II*). A randomised, double-blind, non-inferiority trial. Thromb Haemost 2011, 105: 721-729. 10.1160/TH10-10-0679
Lassen MR, Raskob GE, Gallus A, Pineo G, Chen D, Portman RJ: Apixaban or enoxaparin for thromboprophylaxis after knee replacement. N Engl J Med 2009, 361: 594-604. 10.1056/NEJMoa0810773
Lassen MR, Gallus A, Raskob GE, Pineo G, Chen D, Ramirez LM, Investigators A: Apixaban versus enoxaparin for thromboprophylaxis after hip replacement. N Engl J Med 2010, 363: 2487-2498. 10.1056/NEJMoa1006885
Lassen MR, Raskob GE, Gallus A, Pineo G, Chen D, Hornick P, Investigators A: Apixaban versus enoxaparin for thromboprophylaxis after knee replacement (ADVANCE-2): a randomised double-blind trial. Lancet 2010, 375: 807-815. 10.1016/S0140-6736(09)62125-5
Turpie AG, Kreutz R, Llau J, Norrving B, Haas S: Management consensus guidance for the use of rivaroxaban–an oral, direct factor Xa inhibitor. Thromb Haemost 2012, 108: 876-886. 10.1160/TH12-03-0209
Minet V, Bailly N, Douxfils J, Osselaer JC, Laloy J, Chatelain C, Elalamy I, Chatelain B, Dogne JM, Mullier F: Assessment of the performances of AcuStar HIT and the combination with heparin-induced multiple electrode aggregometry: a retrospective study. Thromb Res 2013, 132: 352-359. 10.1016/j.thromres.2013.06.004
Mullier F, Minet V, Bailly N, Devalet B, Douxfils J, Chatelain C, Elalamy I, Dogne JM, Chatelain B: Platelet microparticle generation assay: a valuable test for immune heparin-induced thrombocytopenia diagnosis. Thromb Res 2014, 133: 1068-1073. 10.1016/j.thromres.2013.12.009
Garg AX, Papaioannou A, Ferko N, Campbell G, Clarke JA, Ray JG: Estimating the prevalence of renal insufficiency in seniors requiring long-term care. Kidney Int 2004, 65: 649-653. 10.1111/j.1523-1755.2004.00412.x
Hellden A, Odar-Cederlof I, Nilsson G, Sjoviker S, Soderstrom A, Euler M, Ohlen G, Bergman U: Renal function estimations and dose recommendations for dabigatran, gabapentin and valaciclovir: a data simulation study focused on the elderly. BMJ Open 2013, 3: e002686.
Maccallum PK, Mathur R, Hull SA, Saja K, Green L, Morris JK, Ashman N: Patient safety and estimation of renal function in patients prescribed new oral anticoagulants for stroke prevention in atrial fibrillation: a cross-sectional study. BMJ Open 2013, 3: e003343.
Adcock DM, Kitchen SO JD, Preston EF: Sample Integrity and Preanalytical Variables. In Quality in Laboratory Hemostasis and Thrombosis. 2nd edition. John Wiley & Sons ed: Blackwell Publishing Ltd; 2013:45-56.
De Caterina R, Husted S, Wallentin L, Andreotti F, Arnesen H, Bachmann F, Baigent C, Huber K, Jespersen J, Kristensen SD: Vitamin K antagonists in heart disease: current status and perspectives (Section III). Position paper of the ESC working group on thrombosis--task force on anticoagulants in heart disease. Thromb Haemost 2013, 110: 1087-1107. 10.1160/TH13-06-0443
Kitchen S, Gray E, Mackie I, Baglin T, Makris M, the Bc: Measurement of non-coumarin anticoagulants and their effects on tests of haemostasis: guidance from the British committee for standards in haematology. Br J Haematol 2014. doi:10.1111/bjh.12975. [Epub ahead of print]
Altman R: New oral anticoagulants: are coagulation units still required? Thromb J 2014, 12: 3. 10.1186/1477-9560-12-3
Contant G, Gouault-Heilmann M, Martinoli JL: Heparin inactivation during blood storage: its prevention by blood collection in citric acid, theophylline, adenosine, dipyridamole-C.T.A.D. mixture. Thromb Res 1983, 31: 365-374. 10.1016/0049-3848(83)90337-7
Ray MJ, Carroll PA, Just SJ, Hawson GA: A low volume specimen container suitable for monitoring the aPTT of heparinized patients. Blood Coagul Fibrinolysis 1993, 4: 805-807. 10.1097/00001721-199310000-00020
Juurlink DN: Drug interactions with warfarin: what clinicians need to know. CMAJ 2007, 177: 369-371. 10.1503/cmaj.070946
Ansell J, Hirsh J, Hylek E, Jacobson A, Crowther M, Palareti G, American College of Chest P: Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest 2008, 133: 160S-198S. 10.1378/chest.08-0670
Quick AJ: The thromboplastin reagent for the determination of Prothrombin. Science 1940, 92: 113-114.
Poller L, Keown M, Chauhan N, van den Besselaar AM, Tripodi A, Shiach C, Jespersen J: European concerted action on anticoagulation. A multicentre calibration study of WHO international reference preparations for thromboplastin, rabbit (RBT/90) and human (rTF/95). J Clin Pathol 2005, 58: 667-669. 10.1136/jcp.2004.019810
Poller L, Thomson JM, Taberner DA, Clarke DK: The correction of coagulometer effects on international normalized ratios: a multicentre evaluation. Br J Haematol 1994, 86: 112-117. 10.1111/j.1365-2141.1994.tb03260.x
Poller L, Jespersen J, Ibrahim S, European Action on A: Warfarin or dabigatran for treatment of atrial fibrillation. J Thromb Haemost 2014, 12: 1193-1195. 10.1111/jth.12590
Poller L, Ibrahim S, Keown M, Pattison A, Jespersen J, European Action On A: The prothrombin time/international normalized ratio (PT/INR) line: derivation of local INR with commercial thromboplastins and coagulometers--two independent studies. J Thromb Haemost 2011, 9: 140-148. 10.1111/j.1538-7836.2010.04109.x
van den Besselaar AM: Artificially depleted plasmas are not necessarily commutable with native patient plasmas for international sensitivity index calibration and international normalized ratio derivation. J Thromb Haemost 2012, 10: 303-305. 10.1111/j.1538-7836.2011.04582.x
Ibrahim S, Jespersen J, Poller L, European Action on A: The clinical evaluation of International normalized ratio variability and control in conventional oral anticoagulant administration by use of the variance growth rate. J Thromb Haemost 2013, 11: 1540-1546. 10.1111/jth.12322
Poller L, Keown M, Chauhan N, van den Besselaar AM, Tripodi A, Jespersen J, Shiach C: European concerted action on anticoagulation. Minimum numbers of lyophilized plasma samples for ISI calibration of CoaguChek and TAS point-of-care whole blood prothrombin time monitors. Am J Clin Pathol 2003, 119: 232-240. 10.1309/25BKYQEP6858GLFD
Christensen TD, Larsen TB: Precision and accuracy of point-of-care testing coagulometers used for self-testing and self-management of oral anticoagulation therapy. J Thromb Haemost 2012, 10: 251-260. 10.1111/j.1538-7836.2011.04568.x
DeSantis G, Hogan-Schlientz J, Liska G, Kipp S, Sallee R, Wurster M, Kupfer K, Ansell J: STABLE results: warfarin home monitoring achieves excellent INR control. Am J Manag Care 2014, 20: 202-209.
Heneghan C, Ward A, Perera R, Self-Monitoring Trialist C, Bankhead C, Fuller A, Stevens R, Bradford K, Tyndel S, Alonso-Coello P: Self-monitoring of oral anticoagulation: systematic review and meta-analysis of individual patient data. Lancet 2012, 379: 322-334. 10.1016/S0140-6736(11)61294-4
Heneghan C, Alonso-Coello P, Garcia-Alamino JM, Perera R, Meats E, Glasziou P: Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. Lancet 2006, 367: 404-411. 10.1016/S0140-6736(06)68139-7
Jowett S, Bryan S, Murray E, McCahon D, Raftery J, Hobbs FD, Fitzmaurice D: Patient self-management of anticoagulation therapy: a trial-based cost-effectiveness analysis. Br J Haematol 2006, 134: 632-639. 10.1111/j.1365-2141.2006.06243.x
Holbrook A, Schulman S, Witt DM, Vandvik PO, Fish J, Kovacs MJ, Svensson PJ, Veenstra DL, Crowther M, Guyatt GH, American College of Chest P: Evidence-based management of anticoagulant therapy: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012, 141: e152S-e184S.
Ufer M: Comparative pharmacokinetics of vitamin K antagonists: warfarin, phenprocoumon and acenocoumarol. Clin Pharmacokinet 2005, 44: 1227-1246. 10.2165/00003088-200544120-00003
Witt DM: Approaches to optimal dosing of vitamin K antagonists. Semin Thromb Hemost 2012, 38: 667-672.
Poller L, Keown M, Ibrahim S, Lowe G, Moia M, Turpie AG, Roberts C, van den Besselaar AM, van der Meer FJ, Tripodi A: A multicentre randomised assessment of the DAWN AC computer-assisted oral anticoagulant dosage program. Thromb Haemost 2009, 101: 487-494.
Ageno W, Gallus AS, Wittkowsky A, Crowther M, Hylek EM, Palareti G, American College of Chest P: Oral anticoagulant therapy: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012, 141: e44S-e88S.
Rosendaal FR, Cannegieter SC, van der Meer FJ, Briet E: A method to determine the optimal intensity of oral anticoagulant therapy. Thromb Haemost 1993, 69: 236-239.
Schulman S, Parpia S, Stewart C, Rudd-Scott L, Julian JA, Levine M: Warfarin dose assessment every 4 weeks versus every 12 weeks in patients with stable international normalized ratios: a randomized trial. Ann Intern Med 2011, 155: 653. -9, W201-3 10.7326/0003-4819-155-10-201111150-00003
Clark NP: Frequency of monitoring, non-adherence, and other topics dear to an anticoagulation clinic provider. J Thromb Thrombolysis 2013, 35: 320-324. 10.1007/s11239-013-0887-y
Rose AJ, Hylek EM, Berlowitz DR, Ash AS, Reisman JI, Ozonoff A: Prompt repeat testing after out-of-range INR values: a quality indicator for anticoagulation care. Circ Cardiovasc Qual Outcomes 2011, 4: 276-282. 10.1161/CIRCOUTCOMES.110.960096
Witt DM, Delate T, Clark NP, Martell C, Tran T, Crowther MA, Garcia DA, Ageno W, Hylek EM, Warped C: Twelve-month outcomes and predictors of very stable INR control in prevalent warfarin users. J Thromb Haemost 2010, 8: 744-749. 10.1111/j.1538-7836.2010.03756.x
Witt DM, Delate T, Clark NP, Martell C, Tran T, Crowther MA, Garcia DA, Ageno W, Hylek EM, Warfarin Associated Research P, other EnDeavors C: Outcomes and predictors of very stable INR control during chronic anticoagulation therapy. Blood 2009, 114: 952-956. 10.1182/blood-2009-02-207928
Rose AJ, Berlowitz DR, Miller DR, Hylek EM, Ozonoff A, Zhao S, Reisman JI, Ash AS: INR targets and site-level anticoagulation control: results from the Veterans AffaiRs Study to Improve Anticoagulation (VARIA). J Thromb Haemost 2012, 10: 590-595. 10.1111/j.1538-7836.2012.04649.x
Sorano GG, Biondi G, Conti M, Mameli G, Licheri D, Marongiu F: Controlled vitamin K content diet for improving the management of poorly controlled anticoagulated patients: a clinical practice proposal. Haemostasis 1993, 23: 77-82.
Kurnik D, Loebstein R, Rabinovitz H, Austerweil N, Halkin H, Almog S: Over-the-counter vitamin K1-containing multivitamin supplements disrupt warfarin anticoagulation in vitamin K1-depleted patients. A prospective, controlled trial. Thromb Haemost 2004, 92: 1018-1024.
Schurgers LJ, Shearer MJ, Hamulyak K, Stocklin E, Vermeer C: Effect of vitamin K intake on the stability of oral anticoagulant treatment: dose-response relationships in healthy subjects. Blood 2004, 104: 2682-2689. 10.1182/blood-2004-04-1525
Reese AM, Farnett LE, Lyons RM, Patel B, Morgan L, Bussey HI: Low-dose vitamin K to augment anticoagulation control. Pharmacotherapy 2005, 25: 1746-1751. 10.1592/phco.2005.25.12.1746
Sconce E, Khan T, Mason J, Noble F, Wynne H, Kamali F: Patients with unstable control have a poorer dietary intake of vitamin K compared to patients with stable control of anticoagulation. Thromb Haemost 2005, 93: 872-875.
Ford SK, Misita CP, Shilliday BB, Malone RM, Moore CG, Moll S: Prospective study of supplemental vitamin K therapy in patients on oral anticoagulants with unstable international normalized ratios. J Thromb Thrombolysis 2007, 24: 23-27. 10.1007/s11239-007-0014-z
Rombouts EK, Rosendaal FR, Van Der Meer FJ: Daily vitamin K supplementation improves anticoagulant stability. J Thromb Haemost 2007, 5: 2043-2048. 10.1111/j.1538-7836.2007.02715.x
Sconce E, Avery P, Wynne H, Kamali F: Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin. Blood 2007, 109: 2419-2423. 10.1182/blood-2006-09-049262
Rombouts EK, Rosendaal FR, van der Meer FJ: Influence of dietary vitamin K intake on subtherapeutic oral anticoagulant therapy. Br J Haematol 2010, 149: 598-605. 10.1111/j.1365-2141.2010.08108.x
Makris M, Watson HG: The management of coumarin-induced over-anticoagulation annotation. Br J Haematol 2001, 114: 271-280. 10.1046/j.1365-2141.2001.02908.x
Hylek EM, Skates SJ, Sheehan MA, Singer DE: An analysis of the lowest effective intensity of prophylactic anticoagulation for patients with nonrheumatic atrial fibrillation. N Engl J Med 1996, 335: 540-546. 10.1056/NEJM199608223350802
Poller L, Jespersen J, Ibrahim S, Pattison A, European Action on A: Phase III studies on novel oral anticoagulants for stroke prevention in atrial fibrillation: a look beyond the excellent results: a rebuttal. J Thromb Haemost 2013, 11: 1203-1205. 10.1111/jth.12164
Dawes J, Bara L, Billaud E, Samama M: Relationship between biological activity and concentration of a low-molecular-weight heparin (PK 10169) and unfractionated heparin after intravenous and subcutaneous administration. Haemostasis 1986, 16: 116-122.
Hirsh J, Raschke R: Heparin and low-molecular-weight heparin: the seventh ACCP conference on antithrombotic and thrombolytic therapy. Chest 2004, 126: 188S-203S. 10.1378/chest.126.3_suppl.188S
Kearon C, Ginsberg JS, Julian JA, Douketis J, Solymoss S, Ockelford P, Jackson S, Turpie AG, MacKinnon B, Hirsh J: Comparison of fixed-dose weight-adjusted unfractionated heparin and low-molecular-weight heparin for acute treatment of venous thromboembolism. JAMA 2006, 296: 935-942. 10.1001/jama.296.8.935
Heit JA, Lahr BD, Petterson TM, Bailey KR, Ashrani AA, Melton LJ 3rd: Heparin and warfarin anticoagulation intensity as predictors of recurrence after deep vein thrombosis or pulmonary embolism: a population-based cohort study. Blood 2011, 118: 4992-4999. 10.1182/blood-2011-05-357343
Zehnder J, Price E, Jin J: Controversies in heparin monitoring. Am J Hematol 2012, 87: S137-S140. 10.1002/ajh.23210
Basu D, Gallus A, Hirsh J, Cade J: A prospective study of the value of monitoring heparin treatment with the activated partial thromboplastin time. N Engl J Med 1972, 287: 324-327. 10.1056/NEJM197208172870703
Garcia DA, Baglin TP, Weitz JI, Samama MM, American College of Chest P: Parenteral anticoagulants: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012, 141: e24S-e43S.
Bates SM, Weitz JI, Johnston M, Hirsh J, Ginsberg JS: Use of a fixed activated partial thromboplastin time ratio to establish a therapeutic range for unfractionated heparin. Arch Intern Med 2001, 161: 385-391. 10.1001/archinte.161.3.385
Gouin-Thibaut I, Martin-Toutain I, Peynaud-Debayle E, Marion S, Napol P, Alhenc-Gelas M: Monitoring unfractionated heparin with APTT: a French collaborative study comparing sensitivity to heparin of 15 APTT reagents. Thromb Res 2012, 129: 666-667. 10.1016/j.thromres.2011.11.016
Bonar RA, Favaloro EJ, Marsden K: External quality assurance for heparin monitoring. Semin Thromb Hemost 2012, 38: 632-639.
Cuker A, Raby A, Moffat KA, Flynn G, Crowther MA: Interlaboratory variation in heparin monitoring: lessons from the quality management program of Ontario coagulation surveys. Thromb Haemost 2010, 104: 837-844. 10.1160/TH10-02-0099
D'Angelo A, Seveso MP, D'Angelo SV, Gilardoni F, Dettori AG, Bonini P: Effect of clot-detection methods and reagents on activated partial thromboplastin time (APTT). Implications in heparin monitoring by APTT. Am J Clin Pathol 1990, 94: 297-306.
Marlar RA, Gausman JN: The effect of instrumentation and laboratory site on the accuracy of the APTT-based heparin therapeutic range. Int J Lab Hematol 2012, 34: 614-620. 10.1111/j.1751-553X.2012.01445.x
Cuker A: Unfractionated heparin for the treatment of venous thromboembolism: best practices and areas of uncertainty. Semin Thromb Hemost 2012, 38: 593-599.
Speer O, Schmugge M, Metzger C, Albisetti M: Reference ranges of coagulation tests. Methods Mol Biol 2013, 992: 85-96. 10.1007/978-1-62703-339-8_6
Olson JD, Arkin CF, Brandt JT, Cunningham MT, Giles A, Koepke JA, Witte DL: College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy: laboratory monitoring of unfractionated heparin therapy. Arch Pathol Lab Med 1998, 122: 782-798.
Hirsh J, Bauer KA, Donati MB, Gould M, Samama MM, Weitz JI, American College of Chest P: Parenteral anticoagulants: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest 2008, 133: 141S-159S. 10.1378/chest.08-0689
Cuker A, Ptashkin B, Konkle BA, Pipe SW, Whinna HC, Zheng XL, Cines DB, Pollak ES: Interlaboratory agreement in the monitoring of unfractionated heparin using the anti-factor Xa-correlated activated partial thromboplastin time. J Thromb Haemost 2009, 7: 80-86. 10.1111/j.1538-7836.2008.03224.x
Despotis GJ, Avidan MS, Hogue CW Jr: Mechanisms and attenuation of hemostatic activation during extracorporeal circulation. Ann Thorac Surg 2001, 72: S1821-S1831. 10.1016/S0003-4975(01)03211-8
Despotis GJ, Joist JH, Goodnough LT: Monitoring of hemostasis in cardiac surgical patients: impact of point-of-care testing on blood loss and transfusion outcomes. Clin Chem 1997, 43: 1684-1696.
Ferraris VA, Ferraris SP, Singh A, Fuhr W, Koppel D, McKenna D, Rodriguez E, Reich H: The platelet thrombin receptor and postoperative bleeding. Ann Thorac Surg 1998, 65: 352-358. 10.1016/S0003-4975(97)01348-9
George JN, Pickett EB, Saucerman S, McEver RP, Kunicki TJ, Kieffer N, Newman PJ: Platelet surface glycoproteins. Studies on resting and activated platelets and platelet membrane microparticles in normal subjects, and observations in patients during adult respiratory distress syndrome and cardiac surgery. J Clin Invest 1986, 78: 340-348. 10.1172/JCI112582
George JN, Shattil SJ: The clinical importance of acquired abnormalities of platelet function. N Engl J Med 1991, 324: 27-39. 10.1056/NEJM199101033240106
Khuri SF, Wolfe JA, Josa M, Axford TC, Szymanski I, Assousa S, Ragno G, Patel M, Silverman A, Park M: Hematologic changes during and after cardiopulmonary bypass and their relationship to the bleeding time and nonsurgical blood loss. J Thorac Cardiovasc Surg 1992, 104: 94-107.
Laffey JG, Boylan JF, Cheng DC: The systemic inflammatory response to cardiac surgery: implications for the anesthesiologist. Anesthesiology 2002, 97: 215-252. 10.1097/00000542-200207000-00030
Levy JH, Tanaka KA: Inflammatory response to cardiopulmonary bypass. Ann Thorac Surg 2003, 75: S715-S720. 10.1016/S0003-4975(02)04701-X
Rinder CS, Bohnert J, Rinder HM, Mitchell J, Ault K, Hillman R: Platelet activation and aggregation during cardiopulmonary bypass. Anesthesiology 1991, 75: 388-393. 10.1097/00000542-199109000-00002
Rinder CS, Mathew JP, Rinder HM, Bonan J, Ault KA, Smith BR: Modulation of platelet surface adhesion receptors during cardiopulmonary bypass. Anesthesiology 1991, 75: 563-570. 10.1097/00000542-199110000-00004
Sniecinski RM, Chandler WL: Activation of the hemostatic system during cardiopulmonary bypass. Anesth Analg 2011, 113: 1319-1333. 10.1213/ANE.0b013e3182354b7e
Warren OJ, Smith AJ, Alexiou C, Rogers PL, Jawad N, Vincent C, Darzi AW, Athanasiou T: The inflammatory response to cardiopulmonary bypass: part 1–mechanisms of pathogenesis. J Cardiothorac Vasc Anesth 2009, 23: 223-231. 10.1053/j.jvca.2008.08.007
Warren OJ, Watret AL, de Wit KL, Alexiou C, Vincent C, Darzi AW, Athanasiou T: The inflammatory response to cardiopulmonary bypass: part 2–anti-inflammatory therapeutic strategies. J Cardiothorac Vasc Anesth 2009, 23: 384-393. 10.1053/j.jvca.2008.09.007
Blombaeck M, Blombaeck B, Wallen P: Determination of the level of heparin in the blood in the case of extracorporeal circulation during cardiac surgery. Rev Hematol 1955, 10: 45-54.
Young JA, Kisker CT, Doty DB: Adequate anticoagulation during cardiopulmonary bypass determined by activated clotting time and the appearance of fibrin monomer. Ann Thorac Surg 1978, 26: 231-240. 10.1016/S0003-4975(10)63676-4
Lobato RL, Despotis GJ, Levy JH, Shore-Lesserson LJ, Carlson MO, Bennett-Guerrero E: Anticoagulation management during cardiopulmonary bypass: a survey of 54 North American institutions. J Thorac Cardiovasc Surg 2010, 139: 1665-1666. 10.1016/j.jtcvs.2010.02.038
Taneja R, Fernandes P, Marwaha G, Cheng D, Bainbridge D: Perioperative coagulation management and blood conservation in cardiac surgery: a Canadian survey. J Cardiothorac Vasc Anesth 2008, 22: 662-669. 10.1053/j.jvca.2008.02.005
Saad EB, Costa IP, Costa RE, Inacio LA Jr, Slater C, Camiletti A, Moura Neto DG, Maldonado P, Camanho LE, Polanczky CA: Safety of ablation for atrial fibrillation with therapeutic INR: comparison with transition to low-molecular-weight heparin. Arq Bras Cardiol 2011, 97: 289-296. 10.1590/S0066-782X2011005000088
Cappato R, Calkins H, Chen SA, Davies W, Iesaka Y, Kalman J, Kim YH, Klein G, Natale A, Packer D: Updated worldwide survey on the methods, efficacy, and safety of catheter ablation for human atrial fibrillation. Circ Arrhythm Electrophysiol 2010, 3: 32-38. 10.1161/CIRCEP.109.859116
Cappato R, Calkins H, Chen SA, Davies W, Iesaka Y, Kalman J, Kim YH, Klein G, Packer D, Skanes A: Worldwide survey on the methods, efficacy, and safety of catheter ablation for human atrial fibrillation. Circulation 2005, 111: 1100-1105. 10.1161/01.CIR.0000157153.30978.67
Calkins H, Kuck KH, Cappato R, Brugada J, Camm AJ, Chen SA, Crijns HJ, Damiano RJ Jr, Davies DW, DiMarco J: 2012 HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: recommendations for patient selection, procedural techniques, patient management and follow-up, definitions, endpoints, and research trial design. J Interv Card Electrophysiol 2012, 33: 171-257. 10.1007/s10840-012-9672-7
Jobes DR, Ellison N, Campbell FW: Limit(ation)s for ACT. Anesth Analg 1989, 69: 142-144.
Jude B, Lasne D, Mouton C, de Moerloose P: Monitoring of heparin therapy during extracorporeal bypass: what are the remaining questions? Ann Fr Anesth Reanim 2004, 23: 589-596. 10.1016/j.annfar.2004.02.047
Hussein HM, Georgiadis AL, Qureshi AI: Point-of-care testing for anticoagulation monitoring in neuroendovascular procedures. AJNR Am J Neuroradiol 2012, 33: 1211-1220. 10.3174/ajnr.A2621
Davidson SJ, Tillyer ML, Keogh J, Hall J, Kelleher AA: Heparin concentrations in neonates during cardiopulmonary bypass. J Thromb Haemost 2012, 10: 730-732. 10.1111/j.1538-7836.2012.04659.x
Gehrie E, Laposata M: Test of the month: the chromogenic antifactor Xa assay. Am J Hematol 2012, 87: 194-196. 10.1002/ajh.22222
Ignjatovic V, Newall F, Monagle P: Heparin concentrations in neonates during cardiopulmonary bypass: a rebuttal. J Thromb Haemost 2012, 10: 1972. 10.1111/j.1538-7836.2012.04796.x
Long E, Pitfield AF, Kissoon N: Anticoagulation therapy: indications, monitoring, and complications. Pediatr Emerg Care 2011, 27: 55-61. quiz2–4 10.1097/PEC.0b013e31820461b1
Jin J, Price E, Nguyen H, Krishnan G, Balise R, Bowen RA, Zehnder JL: Prolonged aPTT relative to Anti-Xa is associated with increased 30-day mortality in hospitalized patients treated with unfractionated Heparin. ASH Annual Meeting Abstracts 2011, 118: 1248.
Alhenc-Gelas M, Jestin-Le Guernic C, Vitoux JF, Kher A, Aiach M, Fiessinger JN: Adjusted versus fixed doses of the low-molecular-weight heparin fragmin in the treatment of deep vein thrombosis. Fragmin-study group. Thromb Haemost 1994, 71: 698-702.
Boneu B, de Moerloose P: How and when to monitor a patient treated with low molecular weight heparin. Semin Thromb Hemost 2001, 27: 519-522. 10.1055/s-2001-17961
Kovacs MJ, Keeney M, MacKinnon K, Boyle E: Three different chromogenic methods do not give equivalent anti-Xa levels for patients on therapeutic low molecular weight heparin (dalteparin) or unfractionated heparin. Clin Lab Haematol 1999, 21: 55-60. 10.1046/j.1365-2257.1999.00183.x
Kitchen S, Iampietro R, Woolley AM, Preston FE: Anti Xa monitoring during treatment with low molecular weight heparin or danaparoid: inter-assay variability. Thromb Haemost 1999, 82: 1289-1293.
Leizorovicz A, Bara L, Samama MM, Haugh MC: Factor Xa inhibition: correlation between the plasma levels of anti-Xa activity and occurrence of thrombosis and haemorrhage. Haemostasis 1993, 23: 89-98.
Hacquard M, Perrin J, Lelievre N, Vigneron C, Lecompte T: Inter-individual variability of effect of 7 low molecular weight antithrombin-dependent anticoagulants studied in vitro with calibrated automated thrombography. Thromb Res 2011, 127: 29-34. 10.1016/j.thromres.2010.07.024
Al Dieri R, Alban S, Beguin S, Hemker HC: Fixed dosage of low-molecular-weight heparins causes large individual variation in coagulability, only partly correlated to body weight. J Thromb Haemost 2006, 4: 83-89.
Potze W, Arshad F, Adelmeijer J, Blokzijl H, van den Berg AP, Porte RJ, Lisman T: Routine coagulation assays underestimate levels of antithrombin-dependent drugs but not of direct anticoagulant drugs in plasma from patients with cirrhosis. Br J Haematol 2013, 163: 666-673. 10.1111/bjh.12593
Bechmann LP, Sichau M, Wichert M, Gerken G, Kroger K, Hilgard P: Low-molecular-weight heparin in patients with advanced cirrhosis. Liver Int 2011, 31: 75-82. 10.1111/j.1478-3231.2010.02358.x
Lisman T, Porte RJ: Towards a rational use of low-molecular-weight heparin in patients with cirrhosis. Liver Int 2011, 31: 1063. 10.1111/j.1478-3231.2011.02489.x
Senzolo M, Rodriguez-Castro KI, Rossetto V, Radu C, Gavasso S, Carraro P, Zerbinati P, Sartori MT, Simioni P: Increased anticoagulant response to low-molecular-weight heparin in plasma from patients with advanced cirrhosis. J Thromb Haemost 2012, 10: 1823-1829. 10.1111/j.1538-7836.2012.04824.x
Tripodi A, Mannucci PM: The coagulopathy of chronic liver disease. N Engl J Med 2011, 365: 147-156. 10.1056/NEJMra1011170
Bates SM, Greer IA, Middeldorp S, Veenstra DL, Prabulos AM, Vandvik PO: VTE, thrombophilia, antithrombotic therapy, and pregnancy: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012, 141: e691S-e736S.
James A: Practice bulletin no. 123: thromboembolism in pregnancy. Obstet Gynecol 2011, 118: 718-729. 10.1097/AOG.0b013e3182310c4c
McLintock C, Brighton T, Chunilal S, Dekker G, McDonnell N, McRae S, Muller P, Tran H, Walters BN, Young L: Recommendations for the diagnosis and treatment of deep venous thrombosis and pulmonary embolism in pregnancy and the postpartum period. Aust N Z J Obstet Gynaecol 2012, 52: 14-22. 10.1111/j.1479-828X.2011.01361.x
Middeldorp S: How I, treat pregnancy-related venous thromboembolism. Blood 2011, 118: 5394-5400. 10.1182/blood-2011-04-306589
Ni Ainle F, Wong A, Appleby N, Byrne B, Regan C, Hassan T, Milner M, Sullivan AO, White B, O'Donnell J: Efficacy and safety of once daily low molecular weight heparin (tinzaparin sodium) in high risk pregnancy. Blood Coagul Fibrinolysis 2008, 19: 689-692. 10.1097/MBC.0b013e32830b14ef
Smith MP, Norris LA, Steer PJ, Savidge GF, Bonnar J: Tinzaparin sodium for thrombosis treatment and prevention during pregnancy. Am J Obstet Gynecol 2004, 190: 495-501. 10.1016/S0002-9378(03)00953-0
Gibson PS, Newell K, Sam DX, Mansoor A, Jiang X, Tang S, Ross S: Weight-adjusted dosing of tinzaparin in pregnancy. Thromb Res 2013, 131: e71-e75. 10.1016/j.thromres.2012.11.018
Morange PE, Alessi MC: Thrombosis in central obesity and metabolic syndrome: mechanisms and epidemiology. Thromb Haemost 2013, 110: 669-680. 10.1160/TH13-01-0075
Frederiksen SG, Hedenbro JL, Norgren L: Enoxaparin effect depends on body-weight and current doses may be inadequate in obese patients. Br J Surg 2003, 90: 547-548. 10.1002/bjs.4068
Nutescu EA, Spinler SA, Wittkowsky A, Dager WE: Low-molecular-weight heparins in renal impairment and obesity: available evidence and clinical practice recommendations across medical and surgical settings. Ann Pharmacother 2009, 43: 1064-1083. 10.1345/aph.1L194
Rowan BO, Kuhl DA, Lee MD, Tichansky DS, Madan AK: Anti-Xa levels in bariatric surgery patients receiving prophylactic enoxaparin. Obes Surg 2008, 18: 162-166. 10.1007/s11695-007-9381-y
Rondina MT, Wheeler M, Rodgers GM, Draper L, Pendleton RC: Weight-based dosing of enoxaparin for VTE prophylaxis in morbidly obese, medically-Ill patients. Thromb Res 2010, 125: 220-223. 10.1016/j.thromres.2009.02.003
Wang TF, Milligan PE, Wong CA, Deal EN, Thoelke MS, Gage BF: Efficacy and safety of high-dose thromboprophylaxis in morbidly obese inpatients. Thromb Haemost 2014, 111: 88-93.
Becker RC, Spencer FA, Gibson M, Rush JE, Sanderink G, Murphy SA, Ball SP, Antman EM: Influence of patient characteristics and renal function on factor Xa inhibition pharmacokinetics and pharmacodynamics after enoxaparin administration in non-ST-segment elevation acute coronary syndromes. Am Heart J 2002, 143: 753-759. 10.1067/mhj.2002.120774
Goudable C, Saivin S, Houin G, Sie P, Boneu B, Tonthat H, Suc JM: Pharmacokinetics of a low molecular weight heparin (Fraxiparine) in various stages of chronic renal failure. Nephron 1991, 59: 543-545. 10.1159/000186641
Cestac P, Bagheri H, Lapeyre-Mestre M, Sie P, Fouladi A, Maupas E, Leger P, Fontan B, Massip P, Montastruc JL: Utilisation and safety of low molecular weight heparins: prospective observational study in medical inpatients. Drug Saf 2003, 26: 197-207. 10.2165/00002018-200326030-00005
Spinler SA, Inverso SM, Cohen M, Goodman SG, Stringer KA, Antman EM: Safety and efficacy of unfractionated heparin versus enoxaparin in patients who are obese and patients with severe renal impairment: analysis from the ESSENCE and TIMI 11B studies. Am Heart J 2003, 146: 33-41. 10.1016/S0002-8703(03)00121-2
Siguret V, Pautas E, Fevrier M, Wipff C, Durand-Gasselin B, Laurent M, Andreux JP, d'Urso M, Gaussem P: Elderly patients treated with tinzaparin (Innohep) administered once daily (175 anti-Xa IU/kg): anti-Xa and anti-IIa activities over 10 days. Thromb Haemost 2000, 84: 800-804.
Mismetti P, Laporte-Simitsidis S, Navarro C, Sie P, d'Azemar P, Necciari J: Aging and venous thromboembolism influence the pharmacodynamics of the anti-factor Xa and anti-thrombin activities of a low molecular weight heparin (nadroparin). Thromb Haemost 1998, 79: 1162-1165.
Schmid P, Brodmann D, Odermatt Y, Fischer AG, Wuillemin WA: Study of bioaccumulation of dalteparin at a therapeutic dose in patients with renal insufficiency. J Thromb Haemost 2009, 7: 1629-1632. 10.1111/j.1538-7836.2009.03556.x
Siguret V, Gouin-Thibault I, Pautas E, Leizorovicz A: No accumulation of the peak anti-factor Xa activity of tinzaparin in elderly patients with moderate-to-severe renal impairment: the IRIS substudy. J Thromb Haemost 2011, 9: 1966-1972. 10.1111/j.1538-7836.2011.04458.x
Bounameaux H, de Moerloose P: Is laboratory monitoring of low-molecular-weight heparin therapy necessary? No. J Thromb Haemost 2004, 2: 551-554. 10.1111/j.1538-7933.2004.00648.x
Harenberg J: Is laboratory monitoring of low-molecular-weight heparin therapy necessary? Yes. J Thromb Haemost 2004, 2: 547-550. 10.1111/j.1538-7933.2004.00647.x
Montalescot G, Collet JP, Tanguy ML, Ankri A, Payot L, Dumaine R, Choussat R, Beygui F, Gallois V, Thomas D: Anti-Xa activity relates to survival and efficacy in unselected acute coronary syndrome patients treated with enoxaparin. Circulation 2004, 110: 392-398. 10.1161/01.CIR.0000136830.65073.C7
Lim W, Dentali F, Eikelboom JW, Crowther MA: Meta-analysis: low-molecular-weight heparin and bleeding in patients with severe renal insufficiency. Ann Intern Med 2006, 144: 673-684. 10.7326/0003-4819-144-9-200605020-00011
Newall F, Chan AK, Ignjatovic V, Monagle P, Perinatal, Paediatric Haemostasis Subcommittee of the S: Recommendations for developing uniform laboratory monitoring of heparinoid anticoagulants in children. J Thromb Haemost 2012, 10: 145-147. 10.1111/j.1538-7836.2011.04561.x
Guyatt GH, Akl EA, Crowther M, Gutterman DD, Schuunemann HJ, American College of Chest Physicians Antithrombotic T: Executive summary: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012, 141: 7S-47S. 10.1378/chest.1412S3
Greene LA, Law C, Jung M, Walton S, Ignjatovic V, Monagle P, Raffini LJ: Lack of anti-factor Xa assay standardization results in significant low molecular weight heparin (enoxaparin) dose variation in neonates and children. J Thromb Haemost 2014. doi: 10.1111/jth.12641. [Epub ahead of print]
Smogorzewska A, Brandt JT, Chandler WL, Cunningham MT, Hayes TE, Olson JD, Kottke-Marchant K, Van Cott EM: Effect of fondaparinux on coagulation assays: results of College of American Pathologists proficiency testing. Arch Pathol Lab Med 2006, 130: 1605-1611.
Samama MM, Martinoli JL, LeFlem L, Guinet C, Plu-Bureau G, Depasse F, Perzborn E: Assessment of laboratory assays to measure rivaroxaban–an oral, direct factor Xa inhibitor. Thromb Haemost 2010, 103: 815-825. 10.1160/TH09-03-0176
Linkins LA, Dans AL, Moores LK, Bona R, Davidson BL, Schulman S, Crowther M, American College of Chest P: Treatment and prevention of heparin-induced thrombocytopenia: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012, 141: e495S-e530S.
Arixtra® (fondaparinux): Monographie du Dictionnaire Vidal. 2012.
Nagler M, Haslauer M, Wuillemin WA: Fondaparinux - data on efficacy and safety in special situations. Thromb Res 2012, 129: 407-417. 10.1016/j.thromres.2011.10.037
GlaxoSmithKline (GSK): Package Insert, Arixtra (Fondaparinux Sodium) Injection. Research Triangle Park, NC: GlaxoSmithKline (GSK); 2004.
Castellone DD, Van Cott EM: Laboratory monitoring of new anticoagulants. Am J Hematol 2010, 85: 185-187.
Cohen D: Dabigatran: how the drug company withheld important analyses. BMJ 2014, 349: g4670-g. 10.1136/bmj.g4670
Reilly PA, Lehr T, Haertter S, Connolly SJ, Yusuf S, Eikelboom JW, Ezekowitz MD, Nehmiz G, Wang S, Wallentin L, Investigators R-L: The effect of dabigatran plasma concentrations and patient characteristics on the frequency of ischemic stroke and major bleeding in atrial fibrillation patients: the RE-LY Trial (Randomized Evaluation of Long-Term Anticoagulation Therapy). J Am Coll Cardiol 2014, 63: 321-328. 10.1016/j.jacc.2013.07.104
Baglin T, Hillarp A, Tripodi A, Elalamy I, Buller H, Ageno W: Measuring Oral Direct Inhibitors (ODIs) of thrombin and factor Xa: a recommendation from the subcommittee on control of anticoagulation of the scientific and standardisation committee of the international society on thrombosis and haemostasis. J Thromb Haemost 2013, 11: 756-760. 10.1111/jth.12149
European Medicine Agency: Pradaxa: summary of product characteristics 2014. [updated 2014 Jul 17; cited 2014 Jul 17]. Available from: http://www.ema.europa.eu/docs/en_GB/document_library/EPAR_-_Product_Information/human/000829/WC500041059.pdf
Douxfils J, Mullier F, Robert S, Chatelain C, Chatelain B, Dogne JM: Impact of dabigatran on a large panel of routine or specific coagulation assays. Laboratory recommendations for monitoring of dabigatran etexilate. Thromb Haemost 2012, 107: 985-997. 10.1160/TH11-11-0804
Van Blerk M, Bailleul E, Chatelain B, Demulder A, Devreese K, Douxfils J, Jochmans K, Mullier F, Wijns W, Soumali MR, Coucke W, Vernelen K, Van de Walle P: Influence of dabigatran and rivaroxaban on routine coagulation assays. A nationwide Belgian survey. Thromb Haemost 2014., 112: [Epub ahead of print]
Lippi G, Salvagno GL, Ippolito L, Franchini M, Favaloro EJ: Shortened activated partial thromboplastin time: causes and management. Blood Coagul Fibrinolysis 2010, 21: 459-463. 10.1097/MBC.0b013e328338dbe8
Kitchen CS: To bleed or not to bleed? Is that the question for the PTT? J Thromb Haemost 2005, 3: 2607-2611. 10.1111/j.1538-7836.2005.01552.x
Eikelboom JW, Hirsh J: Monitoring unfractionated heparin with the aPTT: time for a fresh look. Thromb Haemost 2006, 96: 547-552.
Hirsh J, Warkentin TE, Shaughnessy SG, Anand SS, Halperin JL, Raschke R, Granger C, Ohman EM, Dalen JE: Heparin and low-molecular-weight heparin: mechanisms of action, pharmacokinetics, dosing, monitoring, efficacy, and safety. Chest 2001, 119: 64S-94S. 10.1378/chest.119.1_suppl.64S
Barrett YC, Wang Z, Frost C, Shenker A: Clinical laboratory measurement of direct factor Xa inhibitors: anti-Xa assay is preferable to prothrombin time assay. Thromb Haemost 2010, 104: 1263-1271. 10.1160/TH10-05-0328
Hillarp A, Baghaei F, Fagerberg Blixter I, Gustafsson KM, Stigendal L, Sten-Linder M, Strandberg K, Lindahl TL: Effects of the oral, direct factor Xa inhibitor rivaroxaban on commonly used coagulation assays. J Thromb Haemost 2011, 9: 133-139. 10.1111/j.1538-7836.2010.04098.x
Douxfils J, Mullier F, Loosen C, Chatelain C, Chatelain B, Dogne JM: Assessment of the impact of rivaroxaban on coagulation assays: laboratory recommendations for the monitoring of rivaroxaban and review of the literature. Thromb Res 2012, 130: 956-966. 10.1016/j.thromres.2012.09.004
Douxfils J, Tamigniau A, Chatelain B, Chatelain C, Wallemacq P, Dogne JM, Mullier F: Comparison of calibrated chromogenic anti-Xa assay and PT tests with LC-MS/MS for the therapeutic monitoring of patients treated with rivaroxaban. Thromb Haemost 2013, 110: 723-731. 10.1160/TH13-04-0274
Becker RC, Alexander JH, Newby LK, Yang H, Barrett Y, Mohan P, Wang J, Harrington RA, Wallentin LC: Effect of apixaban, an oral and direct factor Xa inhibitor, on coagulation activity biomarkers following acute coronary syndrome. Thromb Haemost 2010, 104: 976-983. 10.1160/TH10-04-0247
Douxfils J, Chatelain C, Chatelain B, Dogne JM, Mullier F: Impact of apixaban on routine and specific coagulation assays: a practical laboratory guide. Thromb Haemost 2013, 110: 283-294. 10.1160/TH12-12-0898
Frost C, Nepal S, Wang J, Schuster A, Byon W, Boyd RA, Yu Z, Shenker A, Barrett YC, Mosqueda-Garcia R, Lacreta F: Safety, pharmacokinetics and pharmacodynamics of multiple oral doses of apixaban, a factor Xa inhibitor, in healthy subjects. Br J Clin Pharmacol 2013, 76: 776-786. 10.1111/bcp.12106
Gouin-Thibault I, Flaujac C, Delavenne X, Quenet S, Horellou MH, Laporte S, Siguret V, Lecompte T: Assessment of apixaban plasma levels by laboratory tests: suitability of three anti-Xa assays. A multicentre French GEHT study. Thromb Haemost 2014, 111: 240-248.
Barrett YC, Wang Z, Knabb RM: A novel prothrombin time assay for assessing the anticoagulant activity of oral factor Xa inhibitors. Clin Appl Thromb Hemost 2013, 19: 522-528. 10.1177/1076029612441859
van Ryn J, Stangier J, Haertter S, Liesenfeld KH, Wienen W, Feuring M, Clemens A: Dabigatran etexilate--a novel, reversible, oral direct thrombin inhibitor: interpretation of coagulation assays and reversal of anticoagulant activity. Thromb Haemost 2010, 103: 1116-1127. 10.1160/TH09-11-0758
Douxfils J, Dogne JM, Mullier F, Chatelain B, Ronquist-Nii Y, Malmstrom RE, Hjemdahl P: Comparison of calibrated dilute thrombin time and aPTT tests with LC-MS/MS for the therapeutic monitoring of patients treated with dabigatran etexilate. Thromb Haemost 2013, 110: 543-549. 10.1160/TH13-03-0202
Stangier J, Feuring M: Using the HEMOCLOT direct thrombin inhibitor assay to determine plasma concentrations of dabigatran. Blood Coagul Fibrinolysis 2012, 23: 138-143. 10.1097/MBC.0b013e32834f1b0c
Antovic JP, Skeppholm M, Eintrei J, Boija EE, Soderblom L, Norberg EM, Onelov L, Ronquist-Nii Y, Pohanka A, Beck O, Hjemdahl P, Malmström RE: Evaluation of coagulation assays versus LC-MS/MS for determinations of dabigatran concentrations in plasma. Eur J Clin Pharmacol 2013, 69: 1875-1881. 10.1007/s00228-013-1550-4
Hawes EM, Deal AM, Funk-Adcock D, Gosselin R, Jeanneret C, Cook AM, Taylor JM, Whinna HC, Winkler AM, Moll S: Performance of coagulation tests in patients on therapeutic doses of dabigatran: a cross-sectional pharmacodynamic study based on peak and trough plasma levels. J Thromb Haemost 2013, 11: 1493-1502. 10.1111/jth.12308
Nowak G, Ouml TZ: The ecarin clotting time, a universal method to quantify direct thrombin inhibitors. Pathophysiol Haemost Thromb 2003, 33: 173-183. 10.1159/000081505
Gosselin RC, Dwyre DM, Dager WE: Measuring dabigatran concentrations using a chromogenic ecarin clotting time assay. Ann Pharmacother 2013, 47: 1635-1640. 10.1177/1060028013509074
Harenberg J, Kramer R, Giese C, Marx S, Weiss C, Wehling M: Determination of rivaroxaban by different factor Xa specific chromogenic substrate assays: reduction of interassay variability. J Thromb Thrombolysis 2011, 32: 267-271. 10.1007/s11239-011-0622-5
Francart SJ, Hawes EM, Deal AM, Adcock DM, Gosselin R, Jeanneret C, Friedman KD, Moll S: Performance of coagulation tests in patients on therapeutic doses of rivaroxaban. A cross-sectional pharmacodynamic study based on peak and trough plasma levels. Thromb Haemost 2014, 111: 1133-1140. 10.1160/TH13-10-0871
Becker RC, Yang H, Barrett Y, Mohan P, Wang J, Wallentin L, Alexander JH: Chromogenic laboratory assays to measure the factor Xa-inhibiting properties of apixaban--an oral, direct and selective factor Xa inhibitor. J Thromb Thrombolysis 2011, 32: 183-187. 10.1007/s11239-011-0591-8
Harenberg J, Du S, Weiss C, Kramer R, Hoppensteadt D, Walenga J, The working party: methods to determine apixaban of the Subcommittee on Control of Anticoagulation of the International Society of T, Haemostasis: Report of the subcommittee on control of anticoagulation on the determination of the anticoagulant effects of apixaban: communication from the SSC of the ISTH. J Thromb Haemost 2014, 12: 801-804.
The authors declare that they have no competing interests.
JD and FM reviewed the literature, drafted, revised and finalized the manuscript. AT, BC, AG and JMD reviewed the manuscript and commented the scientific content. All authors read and approved the final manuscript.
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Douxfils, J., Tamigniau, A., Chatelain, B. et al. Measurement of non-VKA oral anticoagulants versus classic ones: the appropriate use of hemostasis assays. Thrombosis J 12, 24 (2014). https://doi.org/10.1186/1477-9560-12-24
- Vitamin K antagonist
- Low molecular weight heparin
- Non-VKA oral anticoagulants