Experience with chromogenic substrates in studies of clotting and fibrinolytic systems.

Experiences in the application of chromogenic substrates for the evaluation of clotting variables are reported. The use of a special buffer system enables the determination of factor Xa by the thrombin substrate Chromozym TH. Prothrombin in plasma can be determined using the substrate S-2238 after activation with factor Xa or Ecarin. Factor VII is activated with thromboplastin and is estimated indirectly via factor Xa activity. Comparison of the amidolytic method for factor VII with prothrombin times of patients on oral anticoagulants shows good correlation. Chromogenic substrates can be also used for determining platelet factor 3 (S-2238), plasminogen and alpha 2-antiplasmin.