4Ts score for heparin-induced thrombocytopenia
Four features scored 0-2: degree of thrombocytopenia, timing, thrombosis, other causes. Total 0-8.
Updated · Methodology
About this calculator
The score estimates the pretest probability of heparin-induced thrombocytopenia and answers a practical question: who needs laboratory testing and in whom heparin should be stopped before the result arrives. Four features score 0-2 each, for a total of 0 to 8: 0-3 low probability, 4-5 intermediate, 6-8 high. The strength of the score lies at the low end. At low probability the negative predictive value exceeds 98 % in meta-analyses, which allows heparin to continue and avoids expensive testing. The high end performs less well: the positive predictive value at high probability is moderate, in the range of 20 to 60 % across samples, so a high score leads to stopping heparin and switching to an alternative anticoagulant but does not count as confirmation. On timing: the typical platelet fall occurs on days 5 to 10 after heparin is started, but with heparin exposure in the previous 30 days the fall can happen within a day, and that case also scores 2. Interobserver reproducibility is moderate, which is worth knowing: the item on other causes of thrombocytopenia is the most subjective of the four.
Source
Formula version: lo-2006-v1
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