Performance evaluation of the microINR® point-of-care INR-testing system

IntroductionPoint-of-care International Normalised Ratio (INR) testing is used frequently. We evaluated the microINR((R)) POC system for accuracy, precision and measurement repeatability, and investigated instrument and test chip variability and error rates. MethodsVenous blood INRs of 210 patients on warfarin were obtained with Thromborel((R)) S on the Sysmex CS-2100i((R)) analyser and compared with capillary blood microINR((R)) values. Precision was assessed using control materials. Measurement repeatability was calculated on 51 duplicate finger-prick INRs. Triplicate finger-prick INRs using three different instruments (30 patients) and three different test chip lots (29 patients) were used to evaluate instrument and test chip variability. ResultsLinear regression analysis of microINR((R)) and Sysmex CS2100i((R)) values showed a correlation coefficient of 0.96 (P<.0001) and a positive proportional bias of 4.4%. Dosage concordance was 93.8% and clinical agreement 95.7%. All acceptance criteria based on ISO standard 17593:2007 system accuracy requirements were met. Control material coefficients of variation (CV) varied from 6.2% to 16.7%. The capillary blood measurement repeatability CV was 7.5%. No significant instrument (P=.93) or test chip (P=.81) variability was found, and the error rate was low (2.8%). ConclusionThe microINR((R)) instrument is accurate and precise for monitoring warfarin therapy.