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	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

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 x 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 x 10⁹/L (relative thrombocytopenia).

These findings reflect the fact that the platelet count nadir is dependent on platelet production and platelet consumption. Interestingly, there have been reports in which HIT-associated thrombosis (HITT) was postulated even in the absence of relative thrombocytopenia following cardiovascular surgery.^3-4

In these cases, relative thrombocytopenia was thought to be masked by a supposedly excessive postoperative platelet production. In . . . [Full Text of this Article]

Lorenz Risch, MD; Andreas R. Huber, MD

Correspondence: Dr Huber, Laboratory Medicine, Kantonsspital Aarau, Tellstrasse, CH-5001 Aarau, Switzerland (andreas.huber@ksa.ch).

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