International Normalized Ratio

From Anvita Health Wiki

Contents 1 Introduction 2 Reference-interval 3 Increases 4 Methods 5 More General Terms 6 Additional Terms 7 References

Introduction

• Prothrombin time/normal mean prothrombin time.
  

• Developed in an attempt to standardize prothrombin time measurements accross different laboratories using different reagents.

* 
*           patient PT      ISI 
* INR =  ( --------------- )         
*         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: 3.0-4.0
• 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

• anticoagulation

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]

More General Terms

• clinical coagulation test

Additional Terms

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

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. <PubMed> PMID: [1] <Internet> [2]
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 <PubMed> PMID: [3] <Internet> [4]
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: [5]

International normalized ratio (INR)