Correction of Point-of-Care INR Results in Warfarin Patients.

Background: The measurement of international normalization ratio (INR) may be done by venous blood draw and use of a standard lab, or by fingerstick, using a point of care (POC) device such as the CoaguChek XS^® (Roche Diagnostics), and the CoaguChek XS^® has been validated to meet the International Organization for Standardization (ISO) performance requirements.

Overview: The goal of this study was to determine a correction factor for Coaguchek XS INR levels to a predicted venipuncture (VP) INR level.

Methods: At the end of an anticoagulation clinic visit when a patient had an INR greater than or equal to 4, two INR results existed, that from the Coaguchek XS^® meter and a venipuncture INR from the lab. The data were then discreetly recorded as a quality control for our clinic. The data were analyzed for possible significant trends between the two types of INR results.

Results: The equation that was determined to be the best fit to the data was 0.621 × POC + 0.639 = estimated VP. The overall root mean square error (MSE) for the calculated correction was a 0.44 INR. The root mean square errors were 0.41 and 0.58 for the 4 to 5.9 and 6 to 7.9 POC INR groups, respectively.

Conclusion: The calculation that was derived in this study is not a surrogate for venipuncture INR in this clinic. However, the estimation of the INR may be useful clinically in guiding decision making in the future. (INR, Point of Care, Anticoagulation, Hematology).