Low-molecular-weight heparins and thrombocytosis.

Background: 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.

Methods: 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.

Results: 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).

Conclusions: There is a highly significant association of thrombocytosis reported with LMWH treatment.