What to Know About RA Test Results

Your ankles ache and your fingers are stiff and swollen. Could it be rheumatoid arthritis (RA)? Tests may provide a clue.

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)

Rheumatoid factor (RF) is part of the immune system’s overactive response. It shows up in the blood of about 70% to 80% of people with RA. High levels of it are linked to more severe cases.

Drawbacks: It misses 20% to 30% of cases of RA. It also shows up in other conditions, including:

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.

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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

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.

WebMD Medical Reference Reviewed by David Zelman, MD on May 22, 2019

Sources

SOURCES:

Arthritis Foundation: "Guide to Lab Tests."

Medline Plus, Medical Encyclopedia: "Rheumatoid Factor."

MedicineNet.com: "Rheumatoid Factor."

University of Maryland Medical Center: "Rheumatoid Arthritis - Diagnosis."

The Johns Hopkins Arthritis Center: "RA and Normal Blood Tests."

Lupus Foundation of America: "The Antinuclear Antibody Test: What It Means."

University of Washington, Department of Orthopedics and Sports Medicine: "Lab Tests."

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