Analysis of the One-Stage Test for Prothrombin Time

Abstract

Highly refined prepns. of bovine prothrombin influenced the so-called prothrombin time as detd. by the 1-stage test of Quick to a limited degree only. Modification of concns. of the labile conversion factor and of the stable conversion factor altered the rate of conversion of prothrombin to thrombin in the presence of thromboplastin and Ca. When these conversion factors were kept constant and the concn. of purified prothrombin was varied, the reaction was found to be influenced by changes in titer of prothrombin in the usual way that changes in the concn. of substrate affect reactions between enzyme and substrate; this reaction was minor compared to the changes in prothrombin time invoked by alterations in the concentrations of the accessory conversion factors. It is suggested that the 1-stage tests are in most cases a measure of those factors, labile or stable, which regulate the conversion of prothrombin to thrombin. Since the labile factor is infrequently abnormal, for practical purposes the 1-stage test becomes an assay of the stable factor.