The One-Stage Prothrombin Time: Alterations Due to Changes in Ph

摘要

The study involved the relationship of Factor V lability due to pH variations in the performance of the one-stage prothrombin time. Samples of blood were drawn from ten patients on long-term coumarin-derivative therapy. The pH of each sample was decreased progressively from 7.79 to 6.05 with lactic acid and the prothrombin time was determined. Each sample was then incubated for 4 hours at 37C. and the pH and prothrombin time were measured again on each sample. Factor V activity (BaSO4 absorbed rabbit plasma) and lactic acid were added to the samples in varying order. The addition of lactic acid after incubation did not alter the prothrombin time. The addition of Factor V activity without changing the pH brought the prothrombin time to preincubation values, while subsequent addition of lactic acid to these samples decreased the prothrombin to values less than at preincubation time. The optimal pH for maximal enzyme activity and the mechanism for Factor V lability in the incubated plasma are briefly discussed. (Author)