Summary
Prothrombin has been studied in clotting blood and plasma using the modified 2-stage
prothrombin assay of Ware and Seegers. The quantity as well as the rate of prothrombin
activation has been determined in whole blood and recalcified plasma obtained from
20 normal individuals. A thorough evaluation was made of the techniques used and the
effect of variables such as temperature, surface contact, calcium, platelet concentration,
and pH.
A relatively constant rate of prothrombin activation was observed in clotting blood
and recalcified frozen-thawed plasma.
The results of this study confirm previous investigations of Langdell, Graham, and
Brinkhous using the prothrombin utilization assay. In normal blood, the plasma procoagulants
are found to be present in relative excess in comparison to platelet Factor 3. The
lack of available platelet factor contained in the intact platelets effectively limits
prothrombin activation. Disruption or alteration of the platelets permits the release
of large quantities of platelet Factor 3 and produces a marked increase in the rate
of prothrombin activation.
Glass contact was observed to increase prothrombin activation in blood and plasma.
The use of plasma prothrombin as a substrate for evaluation of procoagulant activity
is discussed and advantages of this system of assay are emphasized.
