What Is the Rheumatoid Factor Test?

If you have the symptoms of rheumatoid arthritis, such as pain, swelling, and stiff joints, your doctor may use the rheumatoid factor blood test to help diagnose it.

This is a simple blood test that measures rheumatoid factor, an antibody that, if it is present, will help your doctor know if you have rheumatoid arthritis. Your body produces antibodies when it detects harmful substances.

The test also helps your doctor tell the difference between rheumatoid arthritis and other types of arthritis, as well as other conditions.

High levels of rheumatoid factor can show up in people with severe rheumatoid arthritis. But even if the test results show you have a high level of it, your doctor will want to do other tests before he makes a diagnosis. He will also examine you and may order other types of lab tests, such as X-rays, an MRI, an ultrasound, or other scans.

How Is It Done?

It’s quick and almost painless. Your doctor will use a needle to collect blood from a vein, and then send your blood sample to a lab for testing.

Preparation

You won’t have to do anything to prepare. Some people are more sensitive than others about having blood taken. If you have questions, talk to your doctor before the test. If you feel faint or nauseated, let your doctor know.

Results

Test results, along with your physical exam, other tests, and your history of symptoms, give your doctor more information and may also help show how serious your rheumatoid arthritis might be.

Remember, sometimes the rheumatoid factor is also found in the blood of healthy people. And it’s found in people with other immune system conditions like lupus and Sjogren's syndrome. People with chronic infections like viral hepatitis can have it too.

WebMD Medical Reference Reviewed by David Zelman, MD on August 25, 2016

Sources

SOURCES:

American Association for Clinical Chemistry: "Rheumatoid Factor."

CDC: "Rheumatoid Arthritis."

National Institute on Arthritis and Musculoskeletal and Skin Diseases (NIAMD): "Rheumatoid Arthritis."

Arthritis Today: "How is Rheumatoid Arthritis Diagnosed?"

Shmerling, R.H, The American Journal of Medicine, 1991.

de Vries-Bouwstra, J.K., Arthritis Rheum, 2008.

McIlwain, H., Pain Free Arthritis, 2003.

American College of Rheumatology: "Rheumatoid Arthritis."

© 2016 WebMD, LLC. All rights reserved.