Measurement of thrombin generation in whole blood--the effect of heparin and aspirin

A technique has been developed to monitor the development of thrombin in freshly collected whole blood in the absence of anticoagulants. It is based on the centrifugal separation of the cellular components from subsamples of blood drawn from non-anticoagulated clotting whole blood which are diluted in buffer containing a chromogenic substrate. It is shown that the burst of thrombin generation after triggering coagulation with trace amounts of tissue thromboplastin occurs sooner in non-anticoagulated whole blood than in citrated whole blood. Heparin is shown to prolong the lag-time of thrombin generation more in native blood than in recalcified citrated blood. It is also demonstrated that intake of 500 mg of aspirin significantly delays and inhibits thrombin generation in non-anticoagulated, thromboplastin triggered whole blood, whereas it has no effect on the coagulation in citrated plasma. The effect of aspirin intake on thrombin generation in blood is roughly equal to that of 0.03 U/ml of unfractionated heparin. This demonstrates that platelet reactions and the coagulation system are closely linked processes. It further lends support to the hypothesis that inhibition of thrombin generation is a common denominator of antithrombotic therapy.