Accuracy and precision of the CoaguChek S versus laboratory INRs in a clinic

BACKGROUND: The CoaguChek S is the next-generation coagulation monitor for measuring the international normalized ratio (INR) that replaces the CoaguChek device. Studies are lacking comparing the CoaguChek S with local laboratory INR assessment to ensure its accuracy and precision for monitoring patients on anticoagulation. OBJECTIVE: To evaluate accuracy, precision, and technical ease-of-use of the CoaguChek S compared with laboratory measurements. METHODS: Accuracy was evaluated in 101 patients by parallel assessment of INRs (CoaguChek S and laboratory); precision was evaluated in 31 patients using duplicate INRs from CoaguChek S and laboratory and from liquid quality controls. Accuracy was determined using orthogonal regression, Bland-Altman plot, and clinical applicability (INRs discrepant in categorization of INR goal and resulting in different therapeutic decisions). Precision was examined by comparing mean difference +/-SD between repeated INRs from CoaguChek S and laboratory, coefficient of variation (CV), and coefficient of repeatability (CR). The influence of low and elevated INRs on accuracy and precision was also examined. To assess ease-of-use of the monitor, the number of technical errors was recorded. RESULTS: The CoaguChek S significantly correlated to laboratory measurement (r = 0.93); 16.7% of INRs resulted in discrepant categorization and 24.5% would have required a different therapeutic plan. The CV and CR compared well between CoaguChek S and laboratory (6% vs. 4.9%; 0.455 vs. 0.346, respectively). When subgroups of INR values <4.0 and <3.0 were evaluated, the precision improved with both methods. Precision, based on liquid quality controls, was good (CV 4.6% = low-level; 3.3% = highlevel). The CoaguChek S was found to have an error rate of 1.8%. CONCLUSIONS: The CoaguChek S is an accurate and precise alternative to laboratory assessment of the INR at values <4.0; it is an efficient device with a low likelihood of errors during testing.