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 ® 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 30-60 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 a mean 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 ® XS Plus POC INR machine is not acceptable for use to monitor patients on warfarin.