A clinical prediction rule used to predict the likelihood (pretest probability) of HIT. Includes a consideration of magnitude of platelet count drop, timing of platelet count drop, presence of thrombosis and presence of alternative causes of the reduced platelet count. See calculator.
Scoring 0, 1, or 2 points for each of 4 categories, maximum possible score = 8 Low score (0-3 points), intermediate score (4 or 5 points), high score (6-8 points).
Low score 0-3 points Intermediate score 4-5 points High score 6-8 points
Low 4Ts score may rule out HIT but high 4Ts score may not be sufficient to diagnose HIT.