Relation between Levels of Plasma Thromboplastin Component (PTC) and Prothrombin Times by the P&P and Quick Methods in Patients Receiving Warfarin

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Abstract
THE coumarin anticoagulants depress the synthesis of four clotting factors: prothrombin; proconvertin (factor VII); Stuart factor (factor X); and plasma thromboplastin component, or PTC (factor IX). Prothrombin times essentially measure an overall effect of the reduced plasma concentration of the first three of these factors. When prothrombin times are used to regulate anticoagulant therapy, one assumes that the level of the unmeasured factor, PTC, does not fall appreciably below the levels of the measured factors.This assumption has been questioned: a disproportionate fall in PTC has been suggested as a possible cause of hemorrhage in patients with prothrombin times within . . .