Normalized Ratio (INR) Determination with a Laboratory-Based System for Control of Oral Anticoagulant Treatment

Objective: To evaluate the accuracy and precision of INR determination of CoaguCheck XS compared to the standard laboratory method among patients with long-term warfarin therapy. Methods: 39 patients receiving long-term warfarin were eligible in this study. Parallel INR measurements were performed. Capillary INR (INR_C) measurements were determined with CoaguCheck XS and venous INR (INR_V) were determined with standard laboratory methods. Results: We found an excellent correlation coefficient (r = 0.968, 95%CI = 0.82 0.99) between INR_V and INR_C among 39 patients receiving long-term warfarin. The mean difference between the two methods was 0.16 (p<0.0001). Although these differences were statistically significant, they were not clinically significant. In 97.4% of the INR parallel measurements the differences between the two methods were within 0.5 INR units. The Bland-Altman difference plot showed greater variation with increasing mean INR values. The coefficient of variation of CoaguCheck XS was 1.07%. Conclusion: The CoaguCheck XS was comparable in accuracy to a standard laboratory method. Its precision was good. It might be a suitable alternative to monitor INR values among patients receiving oral anticoagulants by increasing patient compliance with INR monitoring, and facilitating more frequent INR monitoring especially in highly educated patients.