OBJECTIVE To determine the prevalence of thrombocytopenia in a group of patients suffering from the antiphospholipid syndrome (APS) and to investigate whether these patients may have any particular clinical or serological features.

RESULTS Each of the patients studied had a minimum of three platelet counts during the follow up period. Forty (23.4%) were found to have thrombocytopenia; 13 with persistently low and 27 patients with intermittently low platelet counts. There were no statistically significant differences in sex, age, disease duration or diagnosis when compared with the group of APS patients without thrombocytopenia. Thrombocytopenia was associated with thrombosis in 18, with miscarriages in five, and with both of these features in 13 patients. It was the only manifestation of the APS in four patients. All patients had persistently positive tests for antiphospholipid antibodies concomitantly with the low platelet counts. No significant association was found between the presence of thrombocytopenia and clinical or serological manifestations in APS patients.

CONCLUSION This study showed a prevalence of thrombocytopenia of 23.4% in APS. These patients did not present any significant clinical or serological features that distinguish them from those patients without thrombocytopenia.