Evaluating the Effect of Timing on Point-of-Care Testing of INR

Objectives: To evaluate if there is a difference in International Normalized Ratio (INR) readings taken within the 15 second time frame after lancing the finger vs 30-60 seconds of obtaining a blood drop utilizing a CoaguChek (R) XS Plus point-of-care (POC) INR machine in patients on warfarin therapy. Methods: All adult patients on anticoagulation therapy with warfarin who were managed in a pharmacist-run anticoagulation clinic were considered for inclusion in the study. The mean difference of INR readings taken less than 15 seconds vs between 3060 seconds after the blood drop was obtained from the finger was assessed. Results: A total of 62 pairs of INR results were included in the study. There was amean difference in INR of.076 (95% CI 0.011-.140; P = .0217) when comparing INR readings taken less than 15 seconds and between 30-60 seconds after the blood drop was obtained from the finger. Conclusions: There was a significant difference in INR readings taken less than 15 seconds vs 30-60 seconds after obtaining the blood drop when utilizing a POC INR machine. INR readings taken 30-60 seconds after obtaining a blood drop with the CoaguChek (R) XS Plus POC INR machine is not acceptable for use to monitor patients on warfarin.