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 microINR® POC system for accuracy, precision and measurement repeatability, and investigated instrument and test chip variability and error rates.

METHODS: Venous blood INRs of 210 patients on warfarin were obtained with Thromborel® S on the Sysmex CS-2100i® analyser and compared with capillary blood microINR® 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.

RESULTS: Linear regression analysis of microINR® and Sysmex CS2100i® 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 microINR® instrument is accurate and precise for monitoring warfarin therapy.