Response of Plasma to Excess of Thromboplastin as a Measure of Prothrombin Activity. ∗

Abstract

Summary

1. The response of varying concentrations of stable normal plasma to strong homologous thromboplastin may be expressed by a curve of the parabolic type. Clotting mixtures of high concentration resist activation by thromboplastin, an effect which is more evident with abnormally stable plasmas like those from hemophilics. 2. All current one-stage methods for determining prothrombin activity are done on diluted plasma. The actual plasma concentration in the Quick one-stage procedure is about 26%. 3. In clotting mixtures with a high plasma concentration the action of thromboplastin is resisted, prothrombin conversion is delayed and the rate of clotting of such plasmas cannot be used as an indication of the amount of prothrombin present. Final plasma concentrations of 5% or under in the actual clotting mixture are necessary to be able to derive dependable correlations between the rate of clotting and prothrombin activity. 4. For a full demonstration of plasma anti-cephalin (antithromboplastin) activity, clotting mixtures with a high plasma concentration, a moderately strong homologous thromboplastin and inert contacting surfaces {e.g. silicone) are essential.