The kaolin clotting time; a rapid one-stage method for diagnosis of coagulation defects.

A major variable in blood coagulation tests is the nature and the amount of surface with which the blood comes in contact. When tests on recalcified plasma are used the methods of preparation and storage of the plasma have also to be considered. The prolonged contact of plasma with a large surface, e.g., with glass powder or asbestos, is accompanied by the loss of many coagulation factors, including prothrombin and fibrinogen (Tocantins, 1945). Even a more limited exposure to glass, such as is likely to be encountered in normal practice, may be followed by considerable prolongation of the plasma clotting time (Margolis, 1957). The loss of clotting ability under these conditions is primarily due to the disappearance of the plasma thromboplastin antecedent (Rosenthal, 1955) which is the component most easily destroyed by contact with glass (Margolis, 1958). An additional difficulty when dealing with plasma is that, as the number of platelets decreases with increasing centrifugation, the clotting time becomes more and more sensitive to variations in the platelet count and the results become more unpredictable. Previous investigations (Margolis, 1957) indicated that the clotting time of re-calcified plasma can yield both sensitive and reproducible results when both the contact surface and the platelet content are controlled. The purpose of the present paper is to demonstrate the usefulness of this procedure for the diagnosis of plasma clotting defects.