rheumatoid factor (RF) test, a blood test whose results are positive in approximately 80% of patients with rheumatoid arthritis. Abnormal levels of RF that are lower than those characteristic of rheumatoid arthritis may indicate systemic lupus erythematosus, Sjögren’s syndrome, scleroderma, and other autoimmune conditions. RF is not a useful disease marker because its presence does not disappear in patients who are experiencing a remission from the disease symptoms.
