Evaluation of a coagulation assay determining the activity state of factor VII in plasma

A coagulation assay is described that allows the measurement of the degree of activation of factor VII in circulating blood. The test is based on the use of both bovine and human brain thromboplastin, together with an artificial factor VII-deficient plasma. The latter can be prepared on a relatively large scale which makes it possible to measure factor VII activation in large series of patients. The determination of factor VII activation during incubation at 4 degrees C of plasma of women using oral contraceptives shows that the test described adequately measures factor VII activation. Differences in the time course of factor VII activation during this incubation in glass and plastic containers are found and implicate that rigorous standardization of blood sampling and test conditions is necessary. A possible mechanism that causes this critical dependence upon the test conditions is discussed.