The assay of factor V in plasma using a synthetic chromogenic substrate

An analytical procedure using a synthetic substrate was devised for the determination of factor V in plasma. Factor V was activated by the reaction of immunobilized thrombin and incubated with an optimal concentration of a factor Xa, phospholipid, calcium and prothrombin. The thrombin generated was determined with the chromogenic substrate (Testzym S-2238). The initial rate of hydrolysis of the substrate was directly proportional to the factor V concentration. Effectors in plasma, such as prothrombin, fibrinogen, antithrombins and bilirubin, were controlled to minimize their effects. The normal value of factor V was from 3.3 to 5.5 units.