Maintenance control of oral anticoagulant therapy by an automated chromogenic substrate assay of factor X.

An amidolytic assay of factor X based on the new chromogenic peptide substrate S 2337 (Kabi Diagnostica) was adapted for use with the Kem-o-Mat (Coulter Electronics) automated substrate analyser. Factor X was assayed in 25 healthy controls and in 375 patients on Warfarin therapy. The results in the control group correlated well with a one stage coagulation factor X assay. A good correlation was also found when the S 2337 factor X assay was compared with Thrombotest (Nyegaard & Co.) results in the patients. From the regression line of the S 2337 factor X assay on the Thrombotest results, the comparable range for factor X amidolytic activity in well controlled anticoagulated patients was found to be 22.5-37.5% with this method. Concordant classification of patients by both tests according to proposed therapeutic ranges demonstrated fully concordant information in 76% and fully discordant information in none. This study demonstrates that chromogenic substrate assays for anticoagulant control can be readily automated. Amidolytic assays of factor X based on the S 2337 substrate, therefore, warrant further clinical investigation as a potential method for controlling maintenance oral anticoagulant therapy.