EFFECT OF BLOOD PLATELETS ON PROTHROMBIN UTILIZATION OF DOG AND HUMAN PLASMAS

Abstract

The rate of clotting of dog and human plasmas containing varying numbers of blood platelets was determined. Platelet numbers were reduced to desired levels by centrifugation of blood, without anticoagulant, in silicone-treated apparatus at 2[degree]C. Detns. of the clotting time and the prothrombin utilization rate were made on all blood and plasma samples. The prothrombin utilization rate, i.e., the rate of disappearance of prothrombin from the blood or plasma sample as determined by the 2-stage prothrombin test, was reduced in dog plasmas when the platelet content was below about 35% of the original values. The comparable value for human plasmas was 25%. Clotting time detns. failed to indicate impairment in clotting unless platelets were reduced to below 5-15% of their original numbers. In all expts. human samples required fewer platelets than dog samples for a normal clotting rate. It is concluded that in neither plasma is the number of platelets the factor which determines the rate of clotting. However, platelets do become a limiting factor in the clotting rate if their number is reduced below certain critical levels.