Evolution of a prothrombin conversion accelerator in stored human plasma and prothrombin fractions.

T HE prothrombic activity of plasma, as measured by the one-stage method, decreases as plasma ages (x-3) because of deterioration of ‘labile factor’ necessary for the rapid conversion of prothrombin to thrombin by thromboplastin plus calcium. When, however, determinations are made by a modified procedure in which the test plasma is first diluted with pdkombin-free fresh plasma, the aged plasma shows iru;reased prothrombic activity (3). Similar observations have been recorded by others (4-6). From the data presented below it appears that the phenomenon is referable to the evolution during storage of a factor which can accelerate prothrombin conversion. This substance, similar to or identical with a prothrombin conversion accelerator which is elaborated during coagulation (7), can be separated from stored plasma by adsorbing it with BaS04 from which it can be eluted by sodium citrate.