Analysis of thrombin generation in plasma

Abstract

Thrombin is the central enzyme of haemostasis. Information on the production and inhibition of thrombin in plasma is important for evaluating the state of the coagulation system. Measurement of thrombin generation in plasma using small oligopeptide chromogenic substrates gives rise to a signal that not only reflects the enzymatic activity of free thrombin, but also contains a contribution of the complex of thrombin with one of its inhibitors, alpha 2-macroglobulin. This paper describes a mathematical procedure to extract from the measured curves the signal due to free thrombin only. The time integral of this free thrombin curve, which we call the thrombin potential, is a parameter which condenses much of the information present in such a curve. Thrombin production from prothrombin can be calculated from the concentration of free thrombin, when the rate constants governing the decay of thrombin are known. It is described how this calculation can be performed, accounting for the consumption of some of the inhibitors of thrombin during coagulation. Measurement of the time integral of the thrombin concentration promises clinical applicability of thrombin generation tests. It is based on the continuous registration of conversion of chromogenic substrate by thrombin during coagulation in plasma. It is shown how the curves obtained by this test can be analysed by a procedure which is analogous to the analysis of curves measured by subsampling from clotting plasma.