The rheumatoid factor (RF) test is primarily used to help diagnose rheumatoid arthritis (RA) and to distinguish it from other forms of arthritis and other conditions that cause similar symptoms of joint pain, inflammation, and stiffness. It may be ordered along with other autoimmune-related tests, such as an ANA (antinuclear antibody), along with other markers of inflammation, such as a CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate), and along with a CBC (Complete Blood Count) to evaluate the body’s blood cells. A CCP (Cyclic Citrullinated Peptide Antibody) test, a relatively new test that can help detect early RA, may be ordered if the RF is negative. The RF test may also be ordered, along with tests such as anti-SS-A and anti-SS-B to help diagnose Sjögren’s syndrome.

The test for RF may be ordered when a patient has signs of RA. Symptoms may include pain, warmth, swelling, and morning stiffness in the joints, nodules under the skin, and, if the disease has progressed, evidence on X-rays of swollen joint capsules and loss of cartilage and bone. An RF test may be repeated when the first test is negative and symptoms persist. The RF test also may be ordered when a patient has symptoms suggesting Sjögren’s syndrome. Symptoms may include an extremely dry mouth and eyes, dry skin, and joint and muscle pain. Symptoms may also be mixed as patients may have more than one autoimmune disorder. Patients with RA and/or Sjogren’s syndrome may also have other connective tissue disorders such as Raynaud’s syndrome, scleroderma, autoimmune thyroid disorders, and systemic lupus erythematosis.

In patients with symptoms and clinical signs of rheumatoid arthritis, the presence of significant concentrations of RF indicates that it is likely that they have RA. In patients with the symptoms of Sjögren’s syndrome, significant concentrations of RF indicate that it is likely that they have Sjögren’s.

A negative RF test does not rule out RA or Sjögren’s syndrome. About 20% of patients with RA and many patients with Sjögren’s syndrome will be persistently negative for RF and/or may have very low levels of RF.

Positive RF test results may also be seen in healthy patients and in patients with conditions such as: endocarditis; systemic lupus erythematosus (lupus); tuberculosis; syphilis; sarcoidosis; cancer; viral infection; or disease of the liver, lung, or kidney. The RF test is not used to diagnose or monitor these conditions.

The RF test is not diagnostic or specific. It must be interpreted in conjunction with the patient’s symptoms and history to make a diagnosis of RA, Sjögren’s syndrome, or another condition. The frequency of false positive RF results increases with age.