Abstract
The author 1 developed a quantitative method for the determination of prothrombin based on the principle that the clotting time of blood or plasma is a quantitative measure of the prothrombin concentration provided an excess of thrombin and a constant concentration of calcium are present. For convenience and accuracy, the blood is oxa-lated and the test done on the plasma. It was demonstrated, however, that the test can be applied to whole blood. 2 In this determination 0.1 cc of thromboplastin emulsion was added to 1 cc of blood obtained by venipuncture.
Theoretically there should be essentially no difference between the clotting time of recalcified oxalated plasma and unoxalated plasma or blood provided an excess of thromboplastin is present. This can be demonstrated experimentally as shown by the results of Table I.
Recently Smith and his associates 3 have adopted the author's method of determining the clotting time of 1 cc of blood containing 0.1 cc of thromboplastin as a “Bedside Test” for the determination of pro-thrombin. They employ the formula:
This formula is based on the assumption that the clotting time is a linear function of the concentration of prothrombin. The writer's quantitative studies of prothrombin in man, 4 in the rabbit, in the chicken 5 and other animals have shown that the relationship between the clotting time and the concentration of prothrombin is not linear. If the values are plotted, a hyperbolic curve is obtained which can be satisfactorily expressed by the equation:
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