Use of the Chromogenic Factor X Assay in Patients Transitioning from Argatroban to Warfarin Therapy

Abstract

Study Objective To assess the correlation between the chromogenic factor X assay and the international normalized ratio (INR) in patients transitioning from argatroban to warfarin therapy. Design Retrospective medical record review. Setting Academic medical center and community-based teaching hospital. Patients One hundred thirty-nine patients who had chromogenic factor X levels measured during the transition from argatroban to warfarin therapy between January 1, 2006, and July 31, 2010. Measurements and Main Results The correlation between chromogenic factor X levels and INRs during the transition period was assessed by calculating the sensitivity, specificity, positive predictive value, and negative predictive value for chromogenic factor X levels that were less than or equal to 45% in predicting a therapeutic INR (2.0–3.5). Patients received an average of 4.4 doses of warfarin before argatroban was discontinued. In 60 patients (43.2%), chromogenic factor X levels were subtherapeutic at the time of argatroban discontinuation. Chromogenic factor X levels could predict a therapeutic INR with a sensitivity of 63.2%, a specificity of 80%, a positive predictive value of 93.5, and a negative predictive value of 32.3. In patients who received 5 or more days of warfarin overlap with argatroban, the sensitivity of chromogenic factor X levels to predict an INR greater than 2.0 was 78.2%, with a specificity of 77.8%, a positive predictive value of 95.6, and a negative predictive value of 36.8. The correlation of chromogenic factor X levels and a therapeutic INR was 18.1%; however, this poor correlation may have been due to increases in the INR values of the patients who received less than 5 days of warfarin overlap with argatroban. During the transition period, nine patients developed thrombi and eight patients experienced clinically significant bleeding. Conclusion Measuring chromogenic factor X levels is recommended before transitioning patients from argatroban to warfarin therapy. Patients should receive at least 5 days of overlap with warfarin and have a chromogenic factor X level of 45% or less before discontinuing argatroban.