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

Introduction Point‐of‐care International Normalised Ratio ( INR ) testing is used frequently. We evaluated the micro INR ® POC system for accuracy, precision and measurement repeatability, and investigated instrument and test chip variability and error rates. Methods Venous blood INR s of 210 patients on warfarin were obtained with Thromborel ® S on the Sysmex CS ‐2100i ® analyser and compared with capillary blood micro INR ® values. Precision was assessed using control materials. Measurement repeatability was calculated on 51 duplicate finger‐prick INR s. Triplicate finger‐prick INR s using three different instruments (30 patients) and three different test chip lots (29 patients) were used to evaluate instrument and test chip variability. Results Linear regression analysis of micro INR ® and Sysmex CS 2100i ® 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%). Conclusion The micro INR ® instrument is accurate and precise for monitoring warfarin therapy.