Rheumatoid Factor

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Also known as: RF
Formal name: Rheumatoid Factor

At a Glance

Why Get Tested?

To help diagnose rheumatoid arthritis (RA)

When to Get Tested?

When you have joint pain and fatigue that your health care provider suspects may be due to RA

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


The Test Sample

What is being tested?

Rheumatoid factor (RF) is an autoantibody, an immunoglobulin M (IgM) protein that is produced by the body's immune system. Autoantibodies attack a person's own tissues, mistakenly identifying the tissue as "foreign." While the biologic role of RF is not well understood, its presence is useful as an indicator of inflammatory and autoimmune activity. This test detects and measures RF in the blood.

The RF test is a valuable test for helping to diagnose rheumatoid arthritis (RA). About 80% of those with RA will have a positive RF test. However, RF may also be detected in people with a variety of other disorders, including other autoimmune disorders such as Sjögren syndrome, as well as persistent bacterial, viral, and parasitic infections, and certain cancers. It may sometimes be seen in those with lung disease, liver disease, and kidney disease, and it can be found in a small percentage (1-5%) of healthy people.

How is the sample collected for testing?

A blood sample is collected from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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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

MedlinePlus Medical Encyclopedia. Rheumatoid factor (RF). Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003548.htm. Accessed March 2014.

Mayo Clinic. Rheumatoid factor. Available online at http://www.mayoclinic.com/health/rheumatoid-factor/MY00241 through http://www.mayoclinic.com. Accessed March 2014.

MedicineNet.com. Rheumatoid Factor (RF) Bood Test Results and Significance. Available online at http://www.medicinenet.com/rheumatoid_factor/article.htm through http://www.medicinenet.com. Accessed March 2014.

Quest Diagnostics. Rheumatoid Arthritis Laboratory Markers for Diagnosis and Prognosis. Available online at http://www.questdiagnostics.com/testcenter/testguide.action?dc=CF_RheumatoidArthritis#Test%20Selection through http://www.questdiagnostics.com. Accessed March 2014.

Street T et al. Rheumatoid Factor. Medscape. Available online at http://emedicine.medscape.com/article/2087091-overview#a30 through http://emedicine.medscape.com. Accessed March 2014.

About.com. What Is Rheumatoid Factor? Available online at http://arthritis.about.com/od/radiagnosis/a/rheumfactor.htm through http://arthritis.about.com. Accessed March 2014.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition]. Pp 1681.

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 749-750.

Peng, S. (2005 April 20). Rheumatoid Factor. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003548.htm.

Rindfleisch, J. A. and Muller, D. (2005 September 15). Diagnosis and Management of Rheumatoid Arthritis. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20050915/1037.html through http://www.aafp.org.

(© 2006). Rheumatoid Factor. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_196b.jsp#1147119 through http://www.aruplab.com.

Borigini, M.J. (Updated 2009 May 31). Rheumatoid factor (RF). MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003548.htm. Accessed March 2009.

(Revised 2009 April). Handout on Health: Rheumatoid Arthritis, National Institute of Arthritis and Musculoskeletal and Skin Diseases [On-line information]. Available online at http://www.niams.nih.gov/Health_Info/Rheumatic_Disease/default.asp through http://www.niams.nih.gov. Accessed March 2009.

Borigini, M.J. (Updated 2010 February 7). Rheumatoid Arthritis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000431.htm. Accessed March 2009.

Smith, H. (Updated February 22). Rheumatoid Arthritis. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/331715-overview through http://emedicine.medscape.com. Accessed March 2009.

King, R. and Worthington, R. (Updated 2010 January 12). Arthritis, Rheumatoid. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/808419-overview through http://emedicine.medscape.com. Accessed March 2009.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 825-826.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 958-961.

Sjogrens Syndrome Foundation. About Sjogrens syndrome: Diagnosis. Available online at http://www.sjogrens.org/home/about-sjogrens-syndrome/diagnosis through http://www.sjogrens.org. Accessed May 2010.