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Editor's Correspondence
August 9/23, 2004

Improving the Definition of Heparin-Induced Thrombocytopenia

Arch Intern Med. 2004;164(15):1699. doi:10.1001/archinte.164.15.1699-a

We read with interest the report by Warkentin and colleagues,1 in which the application of a new platelet count fall definition in heparin-induced thrombocytopenia (HIT) revealed twice as many patients to have HIT than originally reported. The improved new definition abandoned the criterion of a fall in platelet count below 150 × 109/L (absolute thrombocytopenia) in postoperative patients, since postoperative thrombocytosis like other preexisting chronic thrombocytosis2 can shift the platelet count nadir following a platelet count fall of 50% or higher to values greater than 150 × 109/L (relative thrombocytopenia).