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Comment & Response
March 24/31, 2020

Confirming Point-of-Care INR Test Results

Author Affiliations
  • 1US Medical and Scientific Affairs, Roche Diagnostics Corporation, Indianapolis, Indiana
JAMA. 2020;323(12):1190-1191. doi:10.1001/jama.2020.0945

To the Editor The authors of the JAMA Diagnostic Test Interpretation article on point-of-care (POC) testing for vitamin K antagonist monitoring suggested confirming POC international normalized ratio (INR) test results greater than 3.5.1 There are numerous INR tests cleared by the US Food and Drug Administration (FDA), and the FDA recommends confirming all POC test results with an INR value greater than 4.5.2 Variation between whole blood POC and citrated plasma-based laboratory methods can be expected. One significant source of variation between INR testing methods is the animal source of thromboplastin. The authors did not mention which specific POC and laboratory assays were used, and therefore it is difficult to know whether the difference observed between the POC and laboratory tests was expected based on differences in thromboplastin.

All INR testing methods do not use the same thromboplastin sources. Comparing INR testing methods using reagents obtained from different animal sources can lead to clinically different results.3,4 There are at least 2 different animal sources of thromboplastin used by the World Health Organization to calibrate POC and laboratory INR testing methods, and anticoagulation management experts have indicated cross-species calibrations are not valid or recommended.5

It is important for health care practitioners using different INR testing methods to know the source of thromboplastin used in each test to judge the accuracy of any POC INR test result and prevent unnecessary blood draws to confirm what may be an expected result.

Section Editor: Jody W. Zylke, MD, Deputy Editor.
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Article Information

Corresponding Author: Corinne R. Fantz, PhD, DABCC, US Medical and Scientific Affairs, Roche Diagnostics Corporation, 9115 Hague Rd, Indianapolis, IN 46250 (corinne.fantz@roche.com).

Conflict of Interest Disclosures: Dr Fantz reported receiving salary support and stocks from Roche Diagnostics Corporation and being a member of the document development committee on POC coagulation testing and anticoagulation monitoring for the Clinical Laboratory Standards Institute.

References
1.
Anderson  I, Wool  GD, Madden  W.  The point-of-care INR test for vitamin K antagonist monitoring.  JAMA. 2019;322(21):2129-2130. doi:10.1001/jama.2019.15720PubMedGoogle ScholarCrossref
2.
Information for health care providers using INR test meters in a clinical setting. US Food and Drug Administration website. Updated February 8, 2018. Accessed January 16, 2020. https://www.fda.gov/medical-devices/warfarin-inr-test-meters/information-health-care-providers-using-inr-test-meters-clinical-setting
3.
Baker  WS, Albright  KJ, Berman  M,  et al.  POCT PT INR—is it adequate for patient care? a comparison of the Roche CoaguChek XS vs. Stago Star vs. Siemens BCS in patients routinely seen in an anticoagulation clinic.  Clin Chim Acta. 2017;472:139-145. doi:10.1016/j.cca.2017.07.027PubMedGoogle ScholarCrossref
4.
Baccouche  H, Chakroun  A, Zoghlami  A, Mahjoub  S, Ben Romdhane  N.  The international normalized ratio (INR): what reagent, what instrument? the assessment of the agreement between INR values according to different reagent/instrument combinations.  J Clin Pharm Ther. 2018;43(1):52-58. doi:10.1111/jcpt.12608PubMedGoogle ScholarCrossref
5.
van den Besselaar  AMHP, Chantarangkul  V, Angeloni  F,  et al.  International collaborative study for the calibration of proposed international standards for thromboplastin, rabbit, plain, and for thromboplastin, recombinant, human, plain.  J Thromb Haemost. 2018;16(1):142-149. doi:10.1111/jth.13879PubMedGoogle ScholarCrossref
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