The concentration of the labile factor of the prothrombin complex in human, dog, and rabbit blood; its significance in the determination of prothrombin activity.

Abstract

Abstract The labile factor of the prothrombin complex is not adsorbed by tricalcium phosphate and similar adsorbents. It disappears from stored oxalated plasma due to destruction by oxidation and this accounts for the decrease of prothrombin activity in stored plasma. A simple method for assaying the labile factor in plasma was developed. The plasma to be assayed is treated with tricalcium phosphate and then the amount is determined which must be added to a fixed quantity of stored human plasma to reduce the prothrombin time to an arbitrarily selected value. By this procedure it was found that rabbit plasma contains fifty times and dog plasma ten times as much labile factor as human plasma. The prothrombin time is reduced to a markedly shorter value when the labile factor is added to stored plasma than when added to fresh plasma, thus suggesting that something is elaborated in stored plasma which increases the activity of the labile factor. The influence of the labile factor on the accuracy of the prothrombin activity determinations and its variations in physiologic and pathologic conditions are discussed.