Prothrombin time

A clotting test, the prothrombin time is done to test the integrity of part of the clotting scheme. The prothrombin time is commonly used as a method of monitoring the accuracy of blood thinning treatment (anticoagulation) with COUMADIN. Familiarly called the "pro time," the test is the time needed for clot formation after a substance called thromboplastin (+ calcium) has been added to plasma. Prothrombin is a coagulation (clotting) factor needed for the normal clotting of blood. There is a cascade of biochemical events that leads to the formation of the final clot. In this cascade, prothrombin is a precursor to thrombin. Because prothrombin comes before thrombin, it is called prothrombin.

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prothrombin time n the time required for a particular specimen of prothrombin to induce blood-plasma clotting under standardized conditions in comparison with a time of between 11.5 and 12 seconds for normal human blood

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(PT)

the time taken for blood clotting to occur in a sample of blood to which calcium and thromboplastin have been added. A prolonged PT (compared with a control sample) indicates a deficiency of coagulation factors, which - with calcium and thromboplastin - are required for the conversion of prothrombin to thrombin to occur in the final stages of blood coagulation. Measurement of PT is used to control anticoagulant therapy (e.g. with warfarin).

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(PT) the rate at which prothrombin is converted to thrombin in citrated blood with added calcium; used to assess the extrinsic pathway of coagulation. Results indicate the integrity of the prothrombin complex, i.e., of factors II, V, VII, and X, and the test is often used to monitor administration of coumarin-type anticoagulants. Called also one-stage prothrombin t., one-stage prothrombin time test, and Quick test.