The ‘4Ts’ score
| Category | 2 points | 1 point | 0 points |
|---|---|---|---|
| Thrombocytopenia | Platelet count drop >50% and nadir ≥20 × 109/L | Platelet count drop 30%–50% or nadir 10–19 × 109/L | Platelet count drop <30% or nadir <10 × 109/L |
| Timing of platelet drop | Onset between days 5–10 or new platelet drop ≥1 day if previous heparin exposure within 30 days | Consistent with day 5–10 drop but unclear (eg missing platelet counts) or onset after 10 days orfall ≤1 day if previous heparin exposure within 30–100 days | Platelet count ≤4 days without recent exposure |
| Thrombosis / other sequelae | New thrombosisorskin necrosis or acute systemic reaction following intravenous UFH bolus | Progressive/recurrent thrombosis or non-necrotising skin lesions or suspected thrombosis (not proven) | None |
| Other causes of thrombocytopenia | No alternative explanation apparent | Possible alternative cause for thrombocytopenia identified | Definite alternative cause for thrombocytopenia |
A score <4 is a low, 4–5 is an intermediate and 6–8 is a high probability of heparin-induced thrombocytopenia. UFH = unfractionated heparin.