Differentiation of thrombin- and factor Xa-related amidolytic activity in plasma by means of a synthetic thrombin inhibitor.

The kinetics of zymogen activation in plasma, upon2$ddition of thromboplastin or partial thromboplastin and Ca may be monitored by continuous measurement of chromophoreirelease from suitable chromogenic substrates. Incorporation of the highly specific thrombin-inhibitor hirudin into the test system allows to differentiate the generation of factor X and thrombin-related amidolytic activity (1). Sti_irzebecher et al. (21, demonstrated that synthetic proteinase inhibitors may improve the specificity of factor X assay procedures using chromogenic substrates by abolishang thrombin interference The aim of the present study was to provide basic concepts for a selective monitoring of activation kinetics and simultaneous estimation of factors involved in the activation pathway, by continuous measurement of factor X and thrombinrelated p-nitroaniline (pNA)-release from a ch?omogenic substrate, in presence and absence of a synthetic thrombin inhibitor.