Rheumatoid Factor (RF) Test

What is a rheumatoid factor (RF) test?

A rheumatoid factor (RF) test measures the amount of rheumatoid factor (RF) in your blood. Rheumatoid factors are proteins produced by the immune system. Normally, the immune system attacks disease-causing substances like viruses and bacteria. Rheumatoid factors attack healthy joints, glands, or other normal cells by mistake.

An RF test is most often used to help diagnose rheumatoid arthritis. Rheumatoid arthritis is a type of autoimmune disorder that causes pain, swelling, and stiffness of the joints. Rheumatoid factors may also be a sign of other autoimmune disorders, such as juvenile arthritis, certain infections, and some types of cancer.

Other names: RF Blood Test

What is it used for?

An RF test is used to help diagnose rheumatoid arthritis or other autoimmune disorders.

Why do I need an RF test?

You may need an RF test if you have symptoms of rheumatoid arthritis. These include:

Joint pain
Joint stiffness, especially in the morning
Joint swelling
Fatigue
Low-grade fever

What happens during an RF test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for an RF test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If rheumatoid factor is found in your blood, it may indicate:

Rheumatoid arthritis
Another autoimmune disease, such lupus, Sjogren's syndrome, juvenile arthritis, or scleroderma
An infection, such as mononucleosis or tuberculosis
Certain cancers, such as leukemia or multiple myeloma

About 20 percent of people with rheumatoid arthritis have little or no rheumatoid factor in their blood. So even if your results were normal, your health care provider may order more tests to confirm or rule out a diagnosis.

If your results were not normal, it doesn't necessarily mean you have a medical condition needing treatment. Some healthy people have rheumatoid factor in their blood, but it's not clear why.

Is there anything else I need to know about an RF test?

An RF test is not used to diagnose osteoarthritis. Although rheumatoid arthritis and osteoarthritis both affect the joints, they are very different diseases. Rheumatoid arthritis is an autoimmune disease that affects people at any age, but usually occurs between the ages of 40 and 60. It affects more women than men. Symptoms may come and go and vary in severity. Osteoarthritis is not an autoimmune disease. It is caused by the wear and tear of joints over time and usually affects adults over the age of 65.

References

Arthritis Foundation [Internet]. Atlanta: Arthritis Foundation; Rheumatoid Arthritis Diagnosis [cited 2018 Feb 28]; [about 4 screens]. Available from: https://www.arthritis.org/about-arthritis/types/rheumatoid-arthritis/diagnosing.php
Arthritis Foundation [Internet]. Atlanta: Arthritis Foundation; Rheumatoid Arthritis Symptoms [cited 2018 Feb 28]; [about 3 screens]. Available from: https://www.arthritis.org/about-arthritis/types/rheumatoid-arthritis/symptoms.php
Arthritis Foundation [Internet]. Atlanta: Arthritis Foundation; What is Osteoarthritis? [cited 2018 Feb 28]; [about 4 screens]. Available from: https://www.arthritis.org/about-arthritis/types/osteoarthritis/what-is-osteoarthritis.php
Arthritis Foundation [Internet]. Atlanta: Arthritis Foundation; What is Rheumatoid Arthritis? [cited 2018 Feb 28]; [about 3 screens]. Available from: https://www.arthritis.org/about-arthritis/types/rheumatoid-arthritis/what-is-rheumatoid-arthritis.php
Hinkle J, Cheever K. Brunner & Suddarth's Handbook of Laboratory and Diagnostic Tests. 2nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Rheumatoid Factor; 460 p.
Johns Hopkins Medicine [Internet]. Johns Hopkins Medicine; Health Library: Rheumatoid Arthritis [cited 2018 Feb 28]; [about 3 screens]. Available from: https://www.hopkinsmedicine.org/healthlibrary/conditions/adult/arthritis_and_other_rheumatic_diseases/rheumatoid_arthritis_85,p01133
Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Arthritis [updated 2017 Sep 20; cited 2018 Feb 28]; [about 3 screens]. Available from: https://labtestsonline.org/conditions/arthritis
Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Rheumatoid Arthritis [updated 2018 Jan 9; cited 2018 Feb 28]; [about 3 screens]. Available from: https://labtestsonline.org/conditions/rheumatoid-arthritis
Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Rheumatoid Factor (RF) [updated 2018 Jan 15; cited 2018 Feb 28]; [about 3 screens]. Available from: https://labtestsonline.org/tests/rheumatoid-factor-rf
Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2018. Rheumatoid Factor; 2017 Dec 30 [cited 2018 Feb 28]; [about 3 screens]. Available from: https://www.mayoclinic.org/tests-procedures/rheumatoid-factor/about/pac-20384800
National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests [cited 2018 Feb 28]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
National Institute of Arthritis and Musculoskeletal and Skin Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Rheumatoid Arthritis [cited 2018 Feb 28]; [about 3 screens]. Available from: https://www.niams.nih.gov/health-topics/rheumatoid-arthritis
University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2018. Health Encyclopedia: Rheumatoid Factor (Blood) [cited 2018 Feb 28]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=rheumatoid_factor
UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Rheumatoid Factor (RF): Results [updated 2017 Oct 10; cited 2018 Feb 28]; [about 8 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/rheumatoid-factor/hw42783.html#hw42811
UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Rheumatoid Factor (RF): Test Overview [updated 2017 Oct 10; cited 2018 Feb 28]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/rheumatoid-factor/hw42783.html

The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.