How Accurate Is The Rheumatoid Factor Test?

Rheumatoid arthritis cannot be diagnosed with a blood test alone. The RF test is helpful in making the diagnosis of RA, but it isn't foolproof. Notably, this test produces both falsepositive and false-negative results.

Rheumatoid arthritis cannot be diagnosed with a blood test alone. The rheumatoid factor test is helpful in making the diagnosis of RA, but it isn't foolproof.

With a false-positive result, a positive RF test doesn't necessarily mean that you have RA. Many reasons other than the presence of RA can cause a person to test positive for RF. For example, the following autoimmune diseases are associated with elevated RF levels:

  • Sj?gren's syndrome
  • Systemic lupus erythematosus
  • Scleroderma
  • Polymyositis/dermatomyositis
  • Mixed connective tissue disease

A variety of infections may also be associated with a positive RF test:

  • Bacterial endocarditis (an infection of the lining of the heart)
  • Osteomyelitis (an infection of the bone)
  • Tuberculosis
  • Syphilis
  • Hepatitis (inflammation of the liver)
  • Mononucleosis

Finally, the following conditions may also produce a positive test for RF:

  • Diffuse interstitial pulmonary fibrosis
  • Liver cirrhosis
  • Sarcoidosis
  • Multiple vaccinations
  • Lipemia (a large amount of fat in the blood)
  • Medication reaction (e.g., methyldopa, a blood pressure drug, can increase the amount of RF detected by the test)
  • Improper handling of the blood specimen
  • An organ transplant from a person not related to you

Several conditions are characterized by painful swollen joints but are not associated with elevated RF levels:

  • Osteoarthritis
  • Ankylosing spondylitis
  • Gout
  • Psoriatic arthritis
  • Reactive arthritis (also known as Reiter's syndrome)

Ankylosing

Crooked or bent; refers to stiffening of the joint.

With a false-negative result, a negative RF test result does not always mean that you do not have RA. Perhaps it is too early in the progression of your disease to detect RF, or you are in a remission phase, or you have a type of RA that occurs without elevated RF levels. In fact, as many as 20% of patients with RA remain negative for RF (also known as “seronegative rheumatoid arthritis”) throughout the course of their disease. For these reasons, if a person tests negative for RF yet continues to have arthritic symptoms, the RF test may need to be repeated. Conversely, if the RF test is positive and the diagnosis of RA is established, there is little benefit in repeating the RF test.

The uncertainty associated with the RF test results is why your doctor needs to take a thorough history and physical exam in addition to administering tests like those for RF, antinuclear antibodies, and x-rays, before he or she can make a definitive diagnosis of RA.