A simple method for the determination of plasma extrinsic coagulant activity

A spectrophotometric study of plasma coagulation is presented with a method for the determination of plasma coagulant activity, via the extrinsic pathway. Dilute citrated plasma was coagulated by recalcification after the addition of a very small amount of thromboplastin. The maximum increase in absorbance per min during coagulation was used as a measure of coagulant activity. The method was applied to normal platelet-rich plasma samples, and the effect of changing the concentration of plasma, thromboplastin, fibrinogen, and heparin was studied.