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Prothrombin Time and International Normalized Ratio

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Also known as: PT; Pro Time; Protime; INR
Formal name: Prothrombin Time and International Normalized Ratio

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

(2014 November 18, Updated). A Patient's Guide to Taking Warfarin. American Heart Association. Available online at http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/A-Patients-Guide-to-Taking-Warfarin_UCM_444996_Article.jsp through http://www.heart.org. Accessed on 4/05/15.

Tuazon, S. and Scarpaci, A. (2014 November 21, Updated). Prothrombin Time. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/2086058-overview through http://emedicine.medscape.com. Accessed on 4/05/15.

Dugdale, D. (2013 February 2, Updated). Prothrombin time (PT). MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003652.htm through http://www.nlm.nih.gov. Accessed on 4/05/15.

(2013 December 18). Blood Thinners. JAMA Patient Page. JAMA v (310) 23. Available online at jama.jamanetwork.com/data/Journals/JAMA/929490/jpg130073.pdf through jama.jamanetwork.com. Accessed on 4/05/15.

Olson, K. and Trickey, D. (2014 November 14, Updated). Warfarin and Superwarfarin Toxicity. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/821038-overview through http://emedicine.medscape.com. Accessed on 4/05/15.

Pagana, K. D., Pagana, T. J., and Pagana, T. N. (© 2015). Mosby's Diagnostic & Laboratory Test Reference 12th Edition: Mosby, Inc., Saint Louis, MO. Pp 767-770.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

(2001). International Normalized Ratio (INR). University Pathology Consortium [On-line handbook]. Available online at http://www.medicine.uiowa.edu/path_handbook/upcmd/01025/inr.html through http://www.medicine.uiowa.edu.

(2000-2004) INR. Northwest Cardiovascular Associates, S.C. [On-line information]. Available online at http://www.nwcardio.com through http://www.nwcardio.com.

Brose, M. (2003 June 1). Prothrombin time (PT). MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003652.htm

Brooke Huffman, G. (2001 April 15). Management of Patients Taking Warfarin. American Family Physician, Tips from other Journals [On-line journal]. Available online at http://www.aafp.org/afp/20010415/tips/5.html through http://www.aafp.org.

Walling, A. (2003 February 15). Optimal Anticoagulation: Determining the Safest INR. American Family Physician, Tips from other Journals [On-line journal]. Available online at http://www.aafp.org/afp/20030215/tips/22.html through http://www.aafp.org.

Miller, K (2003 September 15). Warfarin Management with Mild Elevation of INR. American Family Physician, Tips from other Journals [On-line journal]. Available online at http://www.aafp.org/afp/20030915/tips/6.html through http://www.aafp.org.

Sadovsky, R. (2002 February 15). Factors Affecting the Delay in Return of Therapeutic INR Level. American Family Physician, Tips from other Journals [On-line journal]. Available online at http://www.aafp.org/afp/20020215/tips/12.html through http://www.aafp.org.

Horton, J. and Bushwick, B. (1999 February 1). Warfarin Therapy: Evolving Strategies in Anticoagulation. American Family Physician, Clinical Pharmacology [On-line journal]. Available online at http://www.aafp.org/afp/990201ap/635.html through http://www.aafp.org.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, pp 733-737.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, pp 441-443.

Levin, M. (Updated March 9, 2007) Prothrombin Time (PT). MedlinePlus Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003652.htm. Accessed August 2008.

(Updated May 29, 2007) Prothrombin Time. Massachusetts General Hospital, Pathology Service. Available online at http://www.massgeneral.org/pathology/coagbook/co004400.htm through http://www.massgeneral.org. Accessed August 2008.

(June 2008) Ansell J, et al. Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. 2008 Jun;133(6 Suppl):160S-198S. Available online through http://www.ncbi.nlm.nih.gov. Accessed August 2008.

Heart Rhythm Society. Patient Information, International Normalized Ratio. PDF available for download at http://www.heartrhythmfoundation.org/a-fib/INR_FINAL.pdf through http://www.heartrhythmfoundation.org. Accessed August 2008.

University of Alabama at Birmingham Coagulation Service. Bleeding Guidelines. Available online at http://coag.path.uab.edu/bleeding.htm. Accessed August 2008.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 807-811.

Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 265-281.

Brooks, M. (2012 February 3). Close INR Monitoring Needed When Warfarin Users Add an Antibiotic. Medscape Today News from Reuters Health Information [On-line information]. Available online at http://www.medscape.com/viewarticle/758067 through http://www.medscape.com. Accessed May 2012.

Martin, C. and Beardsell, I. (2012 March 8). Is Routine Coagulation Testing Necessary in Patients Presenting to the Emergency Department With Chest Pain? Medscape News Today from Emerg Med J. 2012;29(3):184-187 [On-line information]. Available online at http://www.medscape.com/viewarticle/759433 through http://www.medscape.com. Accessed May 2012.

Marlar, R. and Gausman, J. (2011 February 23). Do You Report an Accurate International Normalized Ratio? Find Out Using Local Verification and Calibration. Medscape Today News from Lab Med. 2011;42(3):176-181 [On-line information]. Available online at http://www.medscape.com/viewarticle/737622 through http://www.medscape.com. Accessed May 2012.

Dugdale, D. (Updated 2011 February 13). Prothrombin time (PT). MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003652.htm. Accessed May 2012.