Analytical performance of a point-of-care device in monitoring patients on oral anticoagulation with vitamin K antagonists

Abstract

Background [Please check the following sentence for clarity: “Point-of-care devices measuring international normalized ratio have clinical appeal, reports of ‘off-label’ in-hospital/primary care use report improved time to intervention/dose adjustment.”]Point-of-care devices measuring international normalized ratio have clinical appeal, reports of ‘off-label’ in-hospital/primary care use report improved time to intervention/dose adjustment. We evaluated the accuracy and precision of a device for such multiple patient use compared to a reference laboratory. Methods The point-of-care international normalized ratio result of patients on oral anticoagulation at the Vascular Surgery clinic was compared to the reference to check for statistical and clinical correlation. This was a prospective case–control study design with sample size calculated for sensitivity of 87.5%, precision 5% and desired confidence level 95%. Results There were 168 patients tested; 55% were male, the mean age was 45.4. Sixty per cent were in the target international normalized ratio range. Tests were done for statistical and clinical correlation. The international normalized ratio range using the point-of-care device was 0.8–7.5 (reference lab 0.8–10), mean international normalized ratio was 2.22 ± 1.6 (point-of-care device) compared to 2.46 ± 1.3 (reference lab). The mean absolute difference was 0.79 ± 0.92 and the mean relative difference was 8.1% ± 1.03. Data was analysed using a Bland–Altman plot yielding a mean of 0.738 (standard deviation 0.92). Concordance between the tests was 75% with r2 = 0.52 on linear regression. Using an error grid plot, excellent clinical correlation was seen in 63.8%. In 5.4% major corrective action was needed but potentially missed if relying on the point-of-care device. Conclusion The accuracy and precision of this point-of-care device is moderate. It may have potential utility only where access to a reference lab is difficult.