The determination of plasma intrinsic coagulant activity.

Abstract

The increase in absorbance was traced during the coagulation of citrated plasma, while in contact with a plastic cuvette surface. The tracings gave rise to coagulation curves, which provided four values. The coagulation curve values were found to change by time due to contact with the surface of the tube containing the plasma. The rate of change was used to determine the intrinsic coagulant activity, in response to a weak activating surface. The value of the determination as a means for detecting hypercoagulability is discussed. The method was also used to study the effect of different factors affecting intrinsic plasma coagulant activity as ; the surface of different tubes, plasma concentration, temperature of the tube containing the plasma and platelet concentration.-intrinsic coagulant activity ; effect of surface tube ; factors affecting coagulant activity Two plasma coagulant activities can be determined separately in vitro, according to the type of activator used. The extrinsic pathway is activated by the addition of thromboplastin and calcium chloride to citrated plasma, and the intrinsic pathway is activated by calcium chloride and the contact with an active surface (Schmidt 1980). Routine tests, commonly used for the determination of the two activities, are mainly designed to detect the coagulation defects, which cause the prolongation of the clotting time. In these tests, the coagulation cascades are driven at very high velocities, so as deficiencies appear more markedly (Bloom and Thomas 1981). The "prothrombin time" is determined by the addition of an excess amount of thromboplastin, and the extrinsic pathway factors are considered below normal when the clotting time is more than 10-13 sec. The "activated partial thromboplastin time" is determined after the maximal activation of the intrinsic pathway by surface active compounds, to give normal clotting time values between 30-40 sec (Brown 1984). Therefore, the sensitivity of these tests are less suited to measure hypercoagulability, which requires the use of weak activating stimuli. Activation by a weak stimulus prolongs the time of coagulation, and causes the reaction cascades to use their amplification loops (Kwaan and Bowie 1982). Under such conditions the effect of factors causing hyper-