Also Known As
RF
Formal Name
Rheumatoid Factor
This article was last reviewed on
This article waslast modified on March 21, 2018.
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?

None

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

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.

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Common Questions
View Sources

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) Blood 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.

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