Standardization of Laboratory Tests for Controlling Anticoagulant Therapy

Standardization of laboratory methodology for controlling anticoagulation is an important prerequisite to developing uniform guidelines for safe and effective coumarin control. This report describes a method for standardizing thromboplastin reagents by performing parallel tests on specimens from a large group of patients treated with coumarin. By means of least-square regression analysis, results obtained using five rabbit tissue thromboplastins and the ox brain Thrombotest reagent were compared to the results with the Manchester Comparative Reagent (human brain thromboplastin). Although the Manchester and Thrombotest reagents yielded greater discrimination in assaying the “prothrombin complex,” the commercial rabbit tissue reagents appeared sufficiently sensitive to provide safe anticoagulant control. Regardless of the reagent employed, a thorough understanding of the reactivity of the thromboplastin is essential to provide the patient treated with anticoagulants with maximum protection from thrombosis and minimum risk of hemorrhage.