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

Summary A new chromogenic method has been developed and rigorously standardized for the estimation of factor VII in defibrinated diluted plasma. This method employs a mixture of CaCl₂-rabbit brain thromboplastin as activator, diluted factor VII deficient plasma as source of factor X and the chromogenic substrate S2222 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 one-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 five patients with severe congenital factor VII deficiency. A good correlation was also obtained with ‘Thrombotest’. Comparative estimation of factor VII and of 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.