International normalized ratio (INR)
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Introduction
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 interval
- normal value = 1.0
- Therapeutic ranges:
- treatment of deep vein thrombosis, pulmonary embolus, atrial fibrillation or valvular heart disease: 2.0-3.0
- antiphospholipid antibody syndrome: 2.0-3.0[6]
- mechanical prosthetic heart valves* or prevention of recurrent myocardial infarction: 2.5-3.5
- 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
Methods
- point of care testing devices (fingerstick) used at home; comparison with lab testing for monitoring INR for warfarin therapy:
- as effective as in lab testing for reducing thromboembolism
- not as effective as in lab testing for reducing major hemorrhage or mortality[3][4]
- more effective in reducing thromboembolism & mortality[5]
- as effective as in lab testing for reducing major hemorrhage[5]
- 2 point of care tests INRatio & INRatio2 were withdrawn from the market in 2014 over concerns of faulty readings[8]
More general terms
Additional terms
- prothrombin time (PT)
- risk factors for persistently elevated INR
- thromboplastin; tissue factor; TF; coagulation factor III; CD142 (F3)
References
- ↑ Guide to Clinical Laboratory Tests, 3rd ed, NW Teitz (ed) WB Saunders, 1995
- ↑ Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 350
- ↑ 3.0 3.1 Matchar DB et al, Effect of Home Testing of International Normalized Ratio on Clinical Events N Engl J Med 2010 Oct 21; 363:1608. <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/20961244 <Internet> http://www.nejm.org/doi/full/10.1056/NEJMoa1002617
- ↑ 4.0 4.1 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 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/22137798 <Internet> http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)61294-4/fulltext
- ↑ 5.0 5.1 5.2 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: https://www.ncbi.nlm.nih.gov/pubmed/21464349
- ↑ 6.0 6.1 Medical Knowledge Self Assessment Program (MKSAP) 16, American College of Physicians, Philadelphia 2012
- ↑ Mini Panel of 2 tests: Prothrombin Time . International Normalized Ratio Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0030224.jsp
- ↑ 8.0 8.1 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