The 4T's
Estimating the pretest probability of HIT based on clinical features (adapted from Lo et al. 2006)
|
|
2 point |
1 point |
0 point |
|
Thrombocytopenia |
>50% platelet fall (nadir ? 20 x 109/L ) |
30-50% platelet fall (or >50% fall due to surgery); or nadir 10-20 x 109/L | <30% platelet fall; or nadir ? 10 x 109/L |
|
Timing of platelet count fall |
Clear onset between days 5-10 or ? 1 day (if heparin exposure within 30 days) |
Consistent with day 5-10 fall, but not clear (e.g. missing platelet counts) |
Platelet count fall < 4 days without recent heparin exposure |
|
Thrombosis or other sequelae (e.g.skin lesion, acute systemic reactions) |
New thrombosis; skin necrosis; acute systemic reaction following iv heparin bolus |
Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis (not yet proven); asymptomatic upper-limb DVT |
None |
|
Other |
No explanation (besides HIT) for platelet count fall is evident |
Possible other cause is evident |
Definite other cause is present |
Pretest probability score
Score of 6-8 points = high risk of HIT
Score of 4-5 points = moderate risk
Score of 0-3 points = low risk of HIT
1. Lo GK, Juhl D, Warkentin TE et al. Evaluation of pretest clinical score (4T’s) for the diagnosis of heparin–induced thrombocytopenia in two clinical settings. J Thromb Haemost 2006; 4:759-65.
Back to top |
After cardiac surgery |
 |