Platelet clumping in Ph-negative myeloproliferative syndromes.

A retrospective analysis of evidence of platelet clumping, an in vitro phenomenon in blood samples anticoagulated by EDTA, was performed in 49 patients with myeloproliferative diseases other than chronic myeloid leukaemia. Evidence of platelet clumping was provided by the H6000 picture, which in the presence of platelet aggregates yields a characteristic "whisk" in a defined region. Out of the 49 patients, 17 (35%) had evidence of platelet clumping which, however, occurred in an unpredictable manner from time to time. Platelet clumping thus provides a confounding factor when automated platelet counts are used to monitor effects of cytotoxic treatment in this type of disorders. In a prospective study, it was shown that the problem can be overcome by optimizing the hospital routine to secure minimum delay between sampling and analysis.