Platelet aggregation in response to collagen and thrombin reliably detects the ingestion of low-dose aspirin

The exposure of blood donors to aspirin is not reliably excluded by pharmacokinetic measurements due to the irreversible effects of aspirin which persist even after elimination of aspirin and its metabolites from plasma. Tests of platelet functions do overcome this deficit, but are usually limited by substantial inter-individual variability of parameters of platelet function. We have evaluated platelet aggregation ex vivo in 20 aspirin-treated (100 mg single oral dose/day) patients in comparison with a control group of 20 aspirin-free donors. The results demonstrate a significant reduction in the collagen(2.5 micrograms/ml)-induced platelet aggregation by aspirin treatment, whereas thrombin(50 mumol/l TRAP-6)-induced platelet aggregation was not affected at all. Assessment of collagen-induced platelet aggregation relative to platelet responses of the same subject elicited either by thrombin or by a combination of collagen and thrombin does substantially improve the reliability of functional assays of aspirin.