Learn the pros and cons of testing your rheumatoid factor to diagnose rheumatoid arthritis.

If the term “rheumatoid factor” makes you think of rheumatoid arthritis, you’re on the right track: This is a substance in your body that your doctor can measure to see if you may have rheumatoid arthritis.

However, many other conditions may also be associated with higher levels of rheumatoid factor — and people who are healthy may have it, too.

Rheumatoid factor is an antibody that becomes connected to another type of antibody called immunoglobulin, which is an element in your immune system that helps recognize and attack potentially harmful invaders.

Together, these form an immune complex that can become involved in inflammation.

Rheumatoid Factor: How the Test Works

Doctors measure rheumatoid factor by taking a blood sample from a vein using a needle.

Rheumatoid factor is present in about 90 percent of people with rheumatoid arthritis, says Terry Moore, MD, director of rheumatology at Saint Louis University in Missouri. This form of arthritis affects about 1.3 million people in the United States, according to the Arthritis Foundation.

In rheumatoid arthritis, people’s immune systems attack their bodies, causing joint stiffness, pain, and damage. Having a high level of rheumatoid factor may indicate that your immune system is not working properly, according to the Arthritis Foundation.

However, just because your test shows a higher level of rheumatoid factor doesn’t necessarily mean that you have rheumatoid arthritis, says Moore, who has written more than 50 papers on rheumatoid factor as part of his work in researching biomarkers of rheumatoid arthritis. It may also be seen in:

• Many patients with hepatitis B and C
• The elderly
• Children with certain viral infections, such as Epstein-Barr
• People with Sjogren's syndrome
• Lupus patients
• Scleroderma patients

While rheumatoid factor still plays a role in helping diagnose rheumatoid arthritis, Moore says, another test called the anti-CCP test is starting to replace it. This test is useful in many patients with early rheumatoid arthritis, and tends to point out patients with more aggressive disease.

A recent study in the Annals of Internal Medicine that compiled the results of previous studies found that anti-CCP antibodies were more specific for diagnosing rheumatoid arthritis than rheumatoid factor — in other words, the results point more specifically to rheumatoid arthritis than to other diseases.

Rheumatoid Arthritis: Other Tests and Symptoms

If you and your rheumatologist think you may have rheumatoid arthritis, the test for rheumatoid factor will be just one source of information to help your doctor come up with a diagnosis. “When a patient has positive rheumatoid factor, you have to correlate that with other laboratory tests and disease activity. It just doesn't make a diagnosis of rheumatoid arthritis,” Moore says.

Your doctor will also ask you about any symptoms you’ve been having. Possible symptoms of other conditions that may lead to elevated rheumatoid factor include:

• Hepatitis B and C (viral infections affecting the liver): fever, fatigue, nausea, pain in the belly, dark urine, yellow hue in the eyes or skin. In many cases, however, hepatitis C doesn’t cause symptoms.
• Sjogren’s syndrome (an autoimmune disease that can occur along with rheumatoid arthritis): dry eyes and mouth.
• Lupus (another disease in which the immune system attacks the body): joint and muscle pain and a facial rash.
• Scleroderma (a connective tissue disorder): hardening of the skin and pain or tingling in the fingers and toes from reduced blood flow.

It is important that a diagnosis of rheumatoid arthritis be made if your symptoms point to it. Your doctor is the best source for recommending which tests are best for you.