Sex-related differences in platelet aggregation in native whole blood

To clarify discrepant reports about sex-related differences platelet aggregation (PA) was tested by a new impedance method in native whole blood (NWB) and compared to the results of citrated whole blood (CWB) and the turbidometric method (TM). In NWB collagen or ADP-induced PA was stronger in women than men similar to the TM indicating that this is not or not only caused by citrate. With collagen this difference persisted after ingestion of 125 mg acetylsalicylic acid (ASA) which might in part explain the greater therapeutic benefit of ASA for men. The results exclude haematocrit or platelet count as a cause of the differences of PA between women and men. Sodium arachidonate (NaAA)-induced PA was inhibited by 125 mg ASA in all tested methods; since inhibition of ADP-induced PA was not observed in NWB or CWB and the impedance methods failed to show a second wave of ADP-induced PA the significance of the second wave appears doubtful. The impedance method of NWB was found to be more sensitive to collagen, ADP or NaAA than the impedance method of CWB and to collagen or NaAA more sensitive than the TM. The impedance methods in NWB or CWB are not suited to test epinephrine-induced PA.