Low-molecular-weight heparins and thrombocytosis.

Abstract

A possible association between low-molecular-weight heparins (LMWHs) and thrombocytosis was suspected from spontaneous reports to the French Pharmacovigilance System. This association is not mentioned in LMWH's summary of product characteristics. All case records in the French Pharmacovigilance database were reanalyzed for relevance and causality, and the case/noncase approach was used including reports of thrombocytosis as cases and all other reports as noncases. Fifty-one patients treated with LMWHs had platelet counts >500 x 10(3)/mm(3). All patients were asymptomatic, and 1 had a positive rechallenge. There were 143 cases of thrombocytosis among the 174 213 reports in the database, with 61 of 4644 involving LMWHs. The calculated relative reporting ratio is 27.5 (p < 0.0001; 95% CI 19.5 to 38.9). There is a highly significant association of thrombocytosis reported with LMWH treatment.