Rheumatoid Factor

The rheumatoid factor (RF) test is used to help diagnose 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 requested with other autoimmune related tests, such as ANA (antinuclear antibody), markers of inflammation, such as CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate), and with FBC (Full Blood Count) to evaluate the body’s blood cells. 

Cyclic Citrullinated Peptide Antibody (CCP) is a relatively new test that can help detect early RA may be used if RF is negative, and there is a high suspicion of RA. The RF test may also be requested with other autoantibody tests such as anti-Ro (SS-A) and anti-La (SS-B) which help diagnose Sjögren’s syndrome.

The test for RF may be requested 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 requested when a patient has symptoms suggesting Sjögren’s syndrome. Symptoms may include an extremely dry mouth and eyes, and joint and muscle pain. Symptoms may also be mixed as patients may have more than one autoimmune disorder. Sjogren’s syndrome can occur by itself or following RA, or systemic lupus eryhtematosus (SLE). Patients with RA and/or Sjogren’s syndrome may also have other autoimmune disease such as thyroid disorders.

In patients with symptoms and clinical signs of RA the presence of significant concentrations of RF indicates that it is likely that they have rheumatoid arthritis (RA). 70-90% of patients with RA have positive RF test. In patients with symptoms of Sjögren’s syndrome, of the presence of RF can indicate that they have the condition. RF is found in 75-95% of patients with Sjogren’s syndrome. 

A negative RF test does not exclude RA or Sjögren’s syndrome. About 20% of patients with RA or Sjögren’s syndrome will be persistently negative or have low levels of RF.

Positive RF test results may also be seen in healthy patients and in patients with conditions such as: infections; viral infection; endocarditis;; tuberculosis; syphilis; systemic lupus erythematosus (lupus); sarcoidosis; cancer; 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 for RA or Sjögren’s syndrome. It must be interpreted in conjunction with the patient’s symptoms and history, and with tests of inflammation such as ESR or CRP. The frequency of falsely positive RF results increases with as we get older.