A computer assisted method to obtain the prothrombin activation velocity in whole plasma independent of thrombin decay processes.

A method is described that, on the basis of the time course of amidolytic activity after the triggering of thrombin generation in normal plasma, allows the calculation of the velocity of prothrombin conversion independent of thrombin inactivating processes. It is shown how the reaction constants for the alpha 2M-dependent and the alpha 2M-independent thrombin inactivation processes can be obtained in a sample of whole plasma. The method is verified by demonstrating that the experimentally observed time courses of residual prothrombin and of alpha 2M-thrombin complex coincide with those calculated from the time course of amidolytic activity, and by showing that the course of prothrombin conversion in plasma without alpha 2-macroglobulin or AT III is adequately described if the alpha 2M or AT III-dependent breakdown constants are taken zero in the calculations. It appears that the inactivation of thrombin, endogenously generated in whole plasma, is about half as fast as that of exogenous thrombin added to the plasma. A computer program is presented that carries out the relevant calculations.