PERFORMANCE OF PROTHROMBIN-PROCONVERTIN TIME AS A MONITORING TEST OF ORAL ANTICOAGULATION THERAPY

Outcome and anticoagulation intensity was evaluated during 121 patient years of oral anticoagulant therapy monitored with the prothrombin-pr oconvertin clotting time (PP, also known as P&P). The PP-based interna tional normalized ratio (INR; PP-INR) correlated well with the INR cal culated from the prothrombin clotting time (PT; r = 0.92), and results were almost identical over a wide range after linear conversion (1/IN R). When the PP-INR was 4.5 or less, the risk of major bleeding was 1 for every 118 treatment years, but it was 1 for every 73 days when the INR was 6 or more. The 1/PP-INR correlated better with factor II coag ulant activity (r = 0.85) than did the 1/PP-INR (r = 0.78). The 1/PP-I NR also correlated better with the native prothrombin antigen (r = 0.7 6) than did the 1/PP-INR (r = 0.68). The PP and PT results correlated better with factor II coagulant activity than with native prothrombin antigen. Thus, the PP clotting time results can be accurately converte d to INR. The results also suggest that the PP may have advantages ove r the PT as an indicator of anticoagulation intensity during oral anti coagulation.