BACKGROUND: Sex-specific response to antiplatelet medications have been reported in several previous studies.

OBJECTIVE: We investigated a possible connection between gender differences in hemorheological parameters and in vitro platelet aggregation in vascular patients treated with widely used antiplatelet agents.

METHODS: In vitro platelet aggregation was assessed in 2687 patients treated with 100 mg acetylsalicylic acid (ASA), 1047 patients treated with 75 mg clopidogrel and 311 patients on dual antiplatelet therapy (100 mg aspirin and 75 mg clopidogrel) according to the method of Born. In subgroups of patients fibrinogen concentration, whole blood and plasma viscosity, red blood cell aggregation and hematocrit were simultaneously measured. The subjects were divided into groups according to their gender.

RESULTS: ADP induced platelet aggregation was significantly higher in women in the case of ASA treatment (p<0.001). No gender differences could be observed in platelet function in patients treated with clopidogrel or on dual antiplatelet therapy. Hematocrit and whole blood viscosity were significantly higher in men in all groups (p<0.001), while no significant gender differences were observed in red blood cell aggregation indices in either group. Fibrinogen concentration was significantly higher in women than in men among patients treated with 100 mg ASA (p<0.05), but not in the other groups.

CONCLUSIONS: Significantly higher fibrinogen concentration found in aspirin treated women than men may play a role in higher ADP induced platelet aggregation. Gender differences in response to monotherapy suggest that benefits from combination therapy may be greater in females. The clinical relevance of higher ADP induced platelet aggregation in women treated with ASA needs further investigation.