Get the facts about some common lab tests for rheumatoid arthritis—and what they may mean for you.
No single test can diagnose rheumatoid arthritis (RA) or confirm how quickly the disease is progressing. But certain ones can help rule out other diseases and give clues to how well your body is responding to treatment. Here’s a rundown of common RA tests and what the results could mean:
Rheumatoid factor (RF): This antibody is found in the blood of about 80% of people with RA as time goes on—but only 30% in the early stages of the disease, according to the American College of Rheumatology. Therefore, the absence of RF does not rule out the disease.
Anti-CCP antibody: CCP stands for cyclic citrullinated peptide, an antibody that binds to citrulline, an amino acid that is present in 60%-70% of people with RA. A positive anti-CCP may indicate the disease is more likely to progress quickly and increase the risk of joint damage.
Antinuclear antibodies (ANA): These are antibodies that may signal an autoimmune disease, but it’s not unusual for people with RA to test negative. ANA testing may also help rule out other diseases such as lupus and Sjögren’s syndrome.
C-reactive protein: High levels of this protein signal inflammation and injury in the body—an indication of disease activity.
Erythrocyte sedimentation rate (ESR): This is often called your “sed” rate; it’s a measurement of how quickly red blood cells clump together, fall and settle (like sediment) in a test tube. A high ESR indicates more inflammation and more disease activity.
Red blood cell (RBC) count: A low RBC count can signal anemia, a common side effect of RA. However, anemia has many other causes. More severe anemia is often correlated with more severe RA activity.
White blood cell (WBC) count: A low WBC count can occur from a rare side effect of RA, Felty’s syndrome, which is characterized by repeated infections and an enlarged spleen.
Liver and kidney function tests: The liver and kidneys process everything that goes into the body, from food to aspirin. Blood tests can help determine how well your body is processing certain medications, whether used for RA or other conditions.