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

Richter, Christopher PharmD; Taylor, James PharmD; Shuster, Jonathan PhD

Point of Care: The Journal of Near-Patient Testing & Technology: March 2016 - Volume 15 - Issue 1 - p 1–3
doi: 10.1097/POC.0000000000000077
Original Articles

Background The measurement of international normalized ratio (INR) may be performed by venous blood draw and use of a standard laboratory or by fingerstick, using a point-of-care (POC) device such as the CoaguChek XS (Roche Diagnostics, Indianapolis, Ind), and the CoaguChek XS has been validated to meet the International Organization for Standardization 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 of 4 or greater, 2 INR results existed, which were from the Coaguchek XS meter and a VP INR from the laboratory. The data were then discreetly recorded as a quality control for our clinic. The data were analyzed for possible significant trends between the 2 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 for the calculated correction was 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.

Conclusions The calculation that was derived in this study is not a surrogate for VP INR in this clinic. However, the estimation of the INR may be useful clinically in guiding decision making in the future.

From the *Pharmacy Department, UF Health Shands Hospital; †Department of Pharmacotherapy and Translational Research, University of Florida College of Pharmacy; and ‡Department of Health Outcomes, and Biostatistics Epidemiology and Research Design, University of Florida Clinical and Translational Science Institute, Gainesville, FL.

Reprints: Christopher Richter, PharmD, 2000 SW Archer Rd, Room 1520, Gainesville, FL 32610. E-mail:

The authors declare no conflict of interest.

Coaguchek XS machines are used in the UF Health Hematology Anticoagulation Clinic and were provided to the clinic with the purchase of bulk supplies of test strips. There is no bias that will affect the laboratory results and data collection. J. T. is currently receiving a grant from Roche Diagnostics.

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