Effect of aspirin on serum thrombin time and bleeding time.

The present study describes and utilizes a novel method, the serum thrombin time (STT), as a measure of the time for fibrin clot formation in serum following addition of a supramaximal concentration of fibrinogen. The STT and bleeding time (BT) are selectively prolonged in male subjects 2 hours and 24 hours after ingestion of aspirin. In contrast, the STT is unchanged after aspirin ingestion by female subjects. These data indicate that inhibition of cyclooxygenase product formation by aspirin may alter the third stage of coagulation, specifically, endogenous thrombin activity. Furthermore, the ability of aspirin to prolong the STT appears to be sex-specific. Moreover, the STT may be a clinical reflection of endogenous thrombin activity in vivo as well as in vitro and may be of clinical value as a diagnostic probe in the assessment of medical and surgical disorders.