Customize your JAMA Network experience by selecting one or more topics from the list below.
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.
Corresponding Author: Corinne R. Fantz, PhD, DABCC, US Medical and Scientific Affairs, Roche Diagnostics Corporation, 9115 Hague Rd, Indianapolis, IN 46250 (email@example.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.
Fantz CR. Confirming Point-of-Care INR Test Results. JAMA. 2020;323(12):1190–1191. doi:10.1001/jama.2020.0945
Coronavirus Resource Center
Create a personal account or sign in to: