Is there a blood test for rheumatoid arthritis?

There is no single blood test that can diagnose rheumatoid arthritis (RA). However, blood testing is an important part of the diagnosis. Four blood tests may aid in diagnosing RA, along with your history, a physical exam and imaging studies of your joints.

If your history and physical exam suggest a diagnosis of RA, blood testing may be the next step. RA usually starts between the ages of 40 and 60, tends to run in families, and is more common in women.

These are the four most important blood tests:

• Rheumatoid factor (RF) is a protein—also called an antibody—found in up to 80 percent of people with RA. It does not diagnose RA by itself, because some people with RA are not positive for RF, and some people without RA test positive.
• Anti-citrullinated protein antibody (ACPA) is another protein antibody found in 50 to 60 percent of people with RA. It may be an early sign of RA.
• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are both blood tests that measure inflammation. Because active RA causes inflammation, these tests may be done to check for disease activity.

In addition to your history and physical exam, imaging studies of your hands and feet may be done. Your doctor will consider all of these factors when making a diagnosis of RA.