The Four Ts

A new scoring system, the "4 Ts," has been developed that takes advantage of new information regarding the clinical features of HIT (Warkentin, 2003; Warkentin and Heddle, 2003). Platelet count recovery is not a criterion, because this information often is not available at initial evaluation, or heparin may not have been stopped. For simplicity, four clinical features are assessed, given scores of 0, 1, or 2 (Table 7). Thus, the maximal total score is 8.

Estimated pretest probabilities of HIT thereby range from low (0-3) to high (6-8), with an intermediate score (4-5) indicating moderate risk.

Maximal scores for each category are given when the clinical features are highly consistent with HIT. Thus, a patient will score 8 if there is a substantial fall in the platelet count that begins 5-10 days after commencing heparin, together with thrombosis, and where no other plausible cause is apparent during clinical assessment. Even a patient with no clinical evidence of thrombosis can be assigned a high pretest probability (score 6 of 8) if the clinical features are otherwise consistent with HIT. Similarly, a patient can also score high (6 of 8) even in the absence of

TABLE 7 Estimating the Pretest Probability of HIT: "The Four Ts"

Points (0, 1, or 2 for each of 4 categories: maximum possible score = 8)a

TABLE 7 Estimating the Pretest Probability of HIT: "The Four Ts"

0 0

Post a comment