Revised standardization method of the one-stage prothrombin time

The revised ratio method which is recommended for standardization of the one-stage prothrombin time, presumes that identical regression lines exist between clotting times of abnormal and normal plasma. A modification is proposed which corrects for possible deviation of the mean clotting time of normal plasma from the regression line between clotting times of abnormal plasma. The modified revised ration method is theoretically preferable and does not need the restrictions in calibration which are recommended for the revised ratio method.