Table 1.
Estimating the pretest probability of HIT: the “4 T’s”
|
Points (0, 1, or 2 for each of 4 categories: maximum possible score = 8) |
|||
|---|---|---|---|
| 2 | 1 | 0 | |
| Thrombocytopenia | >50% platelet fall to nadir ≥20 | 30%–50% platelet fall or nadir 10–19 | <30% platelet fall or nadir <10 |
| Timinga of onset of platelet fall (or other sequelae of HIT) | 5–10 d or ≤1 d with recent heparin (past 30 d) | >10 d or timing unclear or <1 d with recent heparin (past 30–100 d) | <4 d (no recent heparin) |
| Thrombosis or other sequaele | 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 causes of platelet fall | None evident | Possible | Definite |
a
First day of immunizing heparin exposure considered day 0.
Reprinted with permission from Warkentin TE. Heparin-induced thrombocytopenia: diagnosis and management. Circulation. 2004;110:e454–e458.1 Copyright © 2004 Wolters Kluwer Health.
Notes: Pretest probability score: 6–8 indicates high; 4–5, intermediate; and 0–3, low.
Abbreviations: HIT, heparin-induced thrombocytopenia; UFH, unfractionated heparin.