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International normalized ratio (INR)

Prothrombin time/normal mean prothrombin time. Developed in an attempt to standardize prothrombin time measurements across different laboratories using different reagents. INR = ISI (patient PT / mean control PT) International Sensitivity Index (ISI) depends upon the thromboplastin used in the assay. It varies from 1-2.8. It is generally provided by the manufacturer. Reference values: - normal value = 1.0 - Therapeutic ranges: a) treatment of deep vein thrombosis, pulmonary embolus, atrial fibrillation or valvular heart disease: 2.0-3.0 b) antiphospholipid antibody syndrome: 2.0-3.0 [6] c) mechanical prosthetic heart valves* or prevention of recurrent myocardial infarction: 2.5-3.5 d) treatment of arterial thromboembolism, 1st generation mechanical heart valves (Star-Edwards or Bjork-Shiley) or recurrent systemic embolism: 3.0-4.5 * except 1st generation mechanical heart valves (Star-Edwards or Bjork-Shiley) Increases: - anticoagulation Methods: - point of care testing devices (fingerstick) used at home; comparison with lab testing for monitoring INR for warfarin therapy: a) as effective as in lab testing for reducing thromboembolism b) not as effective as in lab testing for reducing major hemorrhage or mortality [3,4] c) more effective in reducing thromboembolism & mortality [5] d) as effective as in lab testing for reducing major hemorrhage [5] e) 2 point of care tests INRatio & INRatio2 were withdrawn from the market in 2014 over concerns of faulty readings [8]

Related

prothrombin time (PT) risk factors for persistently elevated INR thromboplastin; tissue factor; TF; coagulation factor III; CD142 (F3)

General

clinical coagulation test

References

  1. Guide to Clinical Laboratory Tests, 3rd ed, NW Teitz (ed) WB Saunders, 1995
  2. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 350
  3. Matchar DB et al, Effect of Home Testing of International Normalized Ratio on Clinical Events N Engl J Med 2010 Oct 21; 363:1608. PMID: 20961244 http://www.nejm.org/doi/full/10.1056/NEJMoa1002617
  4. Heneghan C et al Self-monitoring of oral anticoagulation: systematic review and meta-analysis of individual patient data The Lancet, Early Online Publication, 1 December 2011 PMID: 22137798 http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)61294-4/fulltext
  5. Bloomfield HE, Krause A, Greer N, et al. Meta-analysis: effect of patient self-testing and self-management of long-term anticoagulation on major clinical outcomes. Ann Intern Med 2011; 154(7):472-482 PMID: 21464349
  6. Medical Knowledge Self Assessment Program (MKSAP) 16, American College of Physicians, Philadelphia 2012
  7. Mini Panel of 2 tests: Prothrombin Time . International Normalized Ratio Laboratory Test Directory ARUP: 30224
  8. Orciari Herman A. Sadoughi S, Sofair A FDA Examines Safety of INR Point-of-Care Tests Physician's First Watch, March 21, 2016 David G. Fairchild, MD, MPH, Editor-in-Chief Massachusetts Medical Society http://www.jwatch.org