Evaluation of a New Chromogenic Assay for Factor VII and its Application in Patients on Oral Anticoagulant Treatment

Abstract

A new chromogenic method was developed and rigorously standardized for the estimation of factor VII in defibrinated diluted plasma. This method uses a mixture of CaCl2-rabbit brain thromboplastin as activator, diluted factor VII deficient plasma as source of factor X and the chromogenic substrate S 2222 for the measurement of factor Xa. The chromogenic method was insensitive to cold- and kaolin-induced activation of factor VII, this in contrast to the 1-stage clotting assay. Results obtained with the chromogenic method revealed good correlation with the clotting method in 33 normal subjects, in 42 patients on oral anticoagulant therapy and in 5 patients with severe congenital factor VII deficiency. A good correlation was obtained with Thrombotest. Comparative estimation of factor VII and factor VII cross-reacting material in supernatants of BaCl2 adsorbed plasma of coumarin treated patients revealed that the chromogenic method does not measure decarboxy factor VII. Detailed investigations revealed a half life for decarboxy factor VII of 2.1 .+-. 0.6 h.