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Table 1 Calculation of the 4 T Score

From: The potential impact of Covid-19 on the capacity of routine laboratory tests to detect heparin-induced thrombocytopenia

 

Points (0, 1, or 2 for each of the 4 categories: Maximum Possible Score = 8)

2

1

0

Pretest probability score: 6–8 indicates high; 4–5, intermediate; and 0–3, low

aFirst day of immunizing heparin exposure considered day 0

 Thrombocytopenia

 > 50% platelet fall to nadir ≥ 20 G/l

30–50% platelet fall, or nadir 10–19 G/l

 < 30% platelet fall, or nadir < 10

 Timinga of onset of platelet fall (or other sequelae of HIT)

Days 5–10, or ≤ day 1 with recent heparin (past 30 days)

 > Day 10 or timing unclear; or < day 1 with recent heparin (past 31–100 days)

 < Day 4 (no recent heparin)

 Thrombosis or other sequelae

Proven new thrombosis; skin necrosis; or acute systemic reaction after intravenous UFH bolus

Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis (not proven)

None

 Other cause(s) of platelet fall

None evident

Possible

Definitive

  1. Pretest probability score: 6–8: high; 4–5: intermediate; 0–3: low
  2. Selected criteria in the presented case in bold, resulting in a score of 6/8 points
  3. aFirst day of immunising heparin exposure considered day 0