Doctors diagnose RA based largely on your medical history and a physical exam. You may also get lab tests, including the following.
Anti-CCP Antibody Test
This test finds immune system chemicals, called antibodies, that target CCP (cyclic citrullinated peptide), which is present in about 60% to 70% of people with RA. You could have these antibodies years before you get RA symptoms. This test can also predict cases of RA that could become severe.
Drawbacks: It misses 10% to 15% of cases of RA.
Rheumatoid Factor (RF)
Drawbacks: It misses 20% to 30% of cases of RA. It also shows up in other conditions, including:
- Chronic hepatitis
- Chronic viral infection
- Infectious mononucleosis
- Sjogren's syndrome
It’s uncommon, but some healthy people can have RF in their blood test results.
Antinuclear Antibody (ANA) Test
People with lupus often have high levels of these immune system chemicals. So do some, but not all, people with RA.
Drawbacks: By itself, this test does not diagnose RA.
Erythrocyte Sedimentation Rate (ESR, Sed rate)
This test gauges how much inflammation is in the body. It’s usually higher than normal in people with RA and other inflammatory diseases. Doctors may use this test to see whether treatment has lowered inflammation.
Drawbacks: The test doesn’t diagnose RA or any other disease. It also doesn’t show why someone has inflammation.
C-Reactive Protein (CRP)
C-reactive protein is a sign of inflammation. A high CRP could mean someone has an inflammatory disease such as rheumatoid arthritis. But the test doesn’t diagnose any condition.
Many doctors consider it to be a better test than the “sed rate” to measure inflammation. You may get this test to see how well your RA treatment is working.
Drawbacks: Like the sed rate, the CRP test only tells you that there is inflammation. It does not show the cause. Also, not all people with RA have high CRP levels.
Joint Fluid Tests
Sometimes doctors order tests to analyze samples of joint fluid, also called synovial fluid. They remove it from the joint space with a needle.
Drawbacks: This test can’t specifically show that you have RA. But finding fluid with evidence of inflammation supports the diagnosis.
X-rays of the joints help find and track rheumatoid arthritis.
Drawbacks: X-rays aren’t sensitive enough to show early RA damage. And they only show harm to joints and bones, not soft tissue like ligaments, tendons, or muscles.