Comparison of the INR Values Measured by CoaguChek XS Coagulometer and Conventional Laboratory Methods in Patients on VKA Therapy

Background: Warfarin, which is a widely used oral anticoagulant, has a narrow therapeutic window and requires regular international normalized ratio (INR) monitoring to maintain optimal anticoagulation. Recently, several portable coagulometers have been developed to measure INR levels. Objective: To compare the INR results obtained by a portable coagulometer (CoaguChek XS) and a standard laboratory method (STAGO STA-R). Methods: Overall, 433 consecutive patients (male: 191, median age: 61 [44-86] years) who were admitted to outpatient anticoagulation clinic were enrolled in this study. Each patient was tested for INR using portable CoaguChek XS and STAGO STA-R automatic laboratory coagulometer. Correlation between methods was assessed using the Pearson correlation test and Cohen κ test. Bland-Altman plot was used to identify mean difference and 95% limits of agreement. Results: The mean INR values for CoaguChek XS and STAGO STA-R were 2.54 ± 1.17 and 2.79 ± 1.39, respectively. There was a strong positive correlation between the 2 methods (r = .966; 95% confidence interval [CI]: 0.95-0.97, P < .001). The Bland-Altman analysis gave a mean difference of 0.26 ± 0.40 between the 2 methods, with a 95% limit of agreement of −0.54 to 1.05. In patients with INR values >5.0, there was only a moderate correlation (r = .676; 95% CI: 0.38-0.89, P = .002), and the mean difference of INR tended to increase as mean INR values increased. There was a high overall agreement between the 2 methods (κ = .751; 95% CI: 0.69-0.80; P < .001). Conclusion: There was good consistency between traditional laboratory testing and CoaguChek XS coagulometer, which provides rapid and reliable INR analysis.