An inactive substance in the blood PLASMA that is the precursor of the ENZYME, thrombin, which clots the blood. The conversion occurs when a blood vessel is damaged and the process of blood COAGULATION occurs.
n. a substance, present in blood plasma, that is the inactive precursor from which the enzyme *thrombin is derived during the process of *blood coagulation. See also coagulation factors.
(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). See INR.... prothrombin time
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