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Table 20-3

4T Scoring System for Pretest Probability of Heparin-Induced Thrombocytopenia

T Category0 Points1 Point2 Points
ThrombocytopeniaPLT fall <30% or nadir <10 × 109/LPLT fall 30%–50% or nadir 10–19 × 109/LPLT fall >50% and nadir ≥20 × 109/L
Timing of thrombocytopenia≤4 d without prior exposureLikely within 5–10 d, not clear; >10 d; ≤1 d (with exposure 31–100 d)Within 5–10 d of exposure or ≤1 d (with exposure in last 30 d)
Thrombotic eventNo thrombusThrombus recurrence or progression; erythematous skin lesion; suspected thrombusConfirmed thrombus; skin necrosis; acute reaction after UFH bolus
Other causes for thrombocytopeniaDefinitePossibleNone apparent

Sum the points for each of the four categories to determine the clinical probability: high (6–8 points), intermediate (4–5 points), low (0–3 points).

PLT, platelets; UFH, unfractionated heparin.

Data from Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A. Evaluation of pretest clinical score (4 T’s) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost. 2006;4(4):759-765 and Warkentin TE, Linkins LA. Non-necrotizing heparin-induced skin lesions and the 4T’s score. J Thromb Haemost. 2010;8(7):1483-1485.