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International Normalized Ratio

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The International Normalized Ratio (INR) is a "system established by the World Health Organization and the International Committee on Thrombosis and Hemostasis for monitoring and reporting blood coagulation tests. Under this system, results are standardized using the International Sensitivity Index for the particular test reagent/instrument combination used.[1]

It is a computation based on the prothrombin time (PT) and partial thromboplastin time (PTT).

Point-of-care testing

Point-of-care testing of the INR with a sample of blood obtained by fingerstick may[2] or may not[3] be as reliable as an INR measured by a central laboratory. Clinical practice guidelines by the American College of Chest Physicians state "where possible, we suggest that personnel using POC office-based testing participate in proficiency schemes available through professional or national quality assurance organizations".[4]

The CoaguChek system may be more accurate than other POC systems and allows recalibration[5][6]. However, laboratories vary in the performance when using the CoaguChek.[7] External quality assessment is recommended of the CoaguChek.[8]

Self-monitoring of INRs by patients

"Compared to standard monitoring, patients who self-monitor or self-manage can improve the quality of their oral anticoagulation therapy. The number of thromboembolic events and mortality were decreased without increases in harms. However, self-monitoring or self-management were not feasible for up to half of the patients requiring anticoagulant therapy. Reasons included patient refusal, exclusion by their general practitioner, and inability to complete training" according to a meta-analysis by the Cochrane Collaboration. [9]


  1. Anonymous (2019), International Normalized Ratio (English). Medical Subject Headings. U.S. National Library of Medicine.
  2. Bussey HI, Chiquette E, Bianco TM, Lowder-Bender K, Kraynak MA, Linn WD et al. (1997). "A statistical and clinical evaluation of fingerstick and routine laboratory prothrombin time measurements.". Pharmacotherapy 17 (5): 861-6. PMID 9324174[e]
  3. Poller L, Keown M, Chauhan N, van den Besselaar AM, Tripodi A, Shiach C et al. (2003). "Reliability of international normalised ratios from two point of care test systems: comparison with conventional methods.". BMJ 327 (7405): 30. DOI:10.1136/bmj.327.7405.30. PMID 12842954. PMC PMC164241. Research Blogging.
  4. Ansell J, Hirsh J, Hylek E, Jacobson A, Crowther M, Palareti G et al. (2008). "Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition).". Chest 133 (6 Suppl): 160S-198S. DOI:10.1378/chest.08-0670. PMID 18574265. Research Blogging.
  5. Poller L, Keown M, Chauhan N, van den Besselaar AM, Tripodi A, Shiach C et al. (2003). "European Concerted Action on Anticoagulation (ECAA). An assessment of lyophilised plasmas for ISI calibration of CoaguChek and TAS whole blood prothrombin time monitors.". J Clin Pathol 56 (2): 114-9. PMID 12560389. PMC PMC1769887[e]
  6. Poller L, Keown M, Ibrahim SA, van der Meer FJ, van den Besselaar AM, Tripodi A et al. (2006). "Quality assessment of CoaguChek point-of-care prothrombin time monitors: comparison of the European community-approved procedure and conventional external quality assessment.". Clin Chem 52 (10): 1843-7. DOI:10.1373/clinchem.2006.071639. PMID 16998117. Research Blogging.
  7. Cosmi B, Palareti G, Moia M, Carpenedo M, Pengo V, Biasiolo A et al. (2000). "Accuracy of a portable prothrombin time monitor (Coagucheck) in patients on chronic oral anticoagulant therapy: a prospective multicenter study.". Thromb Res 100 (4): 279-86. PMID 11113271[e]
  8. Poller L (2009). "Precision and accuracy of CoaguChek S and XS monitors: the need for external quality assessment.". Thromb Haemost 101 (3): 419-21. DOI:10.1160/TH08-12-0790. PMID 19277400. Research Blogging.
  9. Garcia-Alamino JM, Ward AM, Alonso-Coello P, Perera R, Bankhead C, Fitzmaurice D et al. (2010). "Self-monitoring and self-management of oral anticoagulation.". Cochrane Database Syst Rev (4): CD003839. DOI:10.1002/14651858.CD003839.pub2. PMID 20393937. Research Blogging.