4Ts score HIT calculator

4Ts Score for HIT

4Ts Score for Heparin-Induced Thrombocytopenia

Criteria	0 Points	1 Point	2 Points
Thrombocytopenia	1 <30% fall or nadir <10	30–50% fall or nadir 10–19	>50% fall and nadir ≥20
Timing of platelet fall	1 <4 days without recent heparin	Consistent but unclear; or fall after day 10	5–10 days; or ≤1 day if recent heparin
Thrombosis or other sequelae	1 None	Progressive/recurrent or suspected	Confirmed new thrombosis or skin necrosis
Other causes for thrombocytopenia	1 Definite other cause present	Possible other cause	No other cause apparent
4Ts Score	/ 8

Interpretation — Pretest Probability for HIT

0–3	Low probability (~5% risk of HIT). HIT antibody testing usually not needed.
4–5	Intermediate probability (~14% risk). Send HIT antibody; consider alternative anticoagulation.
6–8	High probability (~64% risk). Start alternative anticoagulant; send confirmatory testing.

References

Lo GK, et al. Evaluation of pretest clinical score (4 Ts) for the diagnosis of heparin-induced thrombocytopenia. J Thromb Haemost. 2006;4(4):759-765. PMID 16634744.