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Rheumatoid factor


The body contains proteins known as antibodies that protect us against infections. Antibodies take part in eliminating foreign and harmful microbes, protecting the body against infections. The body can also produce autoantibodies that bind to the body’s own structures and tissues.

Rheumatoid factor (S-RF) is one such autoantibody, and it binds to the IgG class of antibodies produced by the body. Rheumatoid factor, however, is itself often an autoantibody in the IgM class.

When is a good time to measure the rheumatoid factor value?

Rheumatoid factor can be determined when investigating diseases of the joints and connective tissues. The test can be used in diagnosing a disease, but it is not useful in monitoring the disease.

It can be a good idea to have it tested in connection with the following symptoms:

Joint and muscle pain

  • Intermittent fever
  • Weight loss
  • Swelling and morning stiffness in the joints
  • Lumps under the skin
  • Very dry mouth and eyes
What does a rheumatoid factor test measure?

The test determines whether rheumatoid factor is present in the body. Rheumatoid factor can also occur in healthy individuals, especially elderly people. Rheumatoid factor can also be elevated in many inflammatory diseases and in connection with infections. In addition, not everyone with rheumatic diseases tests positive for rheumatoid factor.

Normally, the result is: 

Reference values:

  • Negative: <14 U/ml

The rheumatoid factor result can be negative for approximately one in three people with rheumatoid arthritis. The rheumatoid factor test does not therefore fully indicate the state of rheumatoid arthritis; the test result must be interpreted together with the symptoms and the patient’s history and other tests.

The other tests used when suspecting rheumatoid arthritis are C-reactive protein (S-CRP), ESR (B-La), and citrullinated peptide antibodies (S-CCPAb), which together enhance diagnostics.

Please contact your physician or other healthcare professional if you suspect an illness or need help interpreting the results.

Read more about defining reference values.

A positive rheumatoid factor result can occur in the following contexts:

  • Rheumatoid arthritis (approximately 80–90%)
  • Sjögren's syndrome (75%)
  • Systemic lupus erythematosus, or SLE (30–40%)
  • Dermatomyositis
  • Polyarteritis nodosa

A positive rheumatoid factor is also possible in connection with the following diseases:

  • Sudden inflammatory diseases (such as mononucleosis, endocarditis, and hepatitis)
  • Joint inflammation during or after (reactive) bacterial inflammation
  • Connective tissue disease
  • Diseases of the liver and lungs
  • Chronic inflammation

The rheumatoid factor test is not used for diagnosing or monitoring the above-mentioned conditions.

Rheumatoid factor is normally negative, meaning that it is not present in the body or is present in miniscule amounts.

  • C-reactive protein indicates sudden and bacterial infections (8022 S-hsCRP)
  • ESR indicates chronic and viral infections (2203 B-La)
  • Citrullinated peptide antibodies are always present in connection with rheumatoid arthritis (4744 S-CCPAb)


Fasting is not required

This examination does not require fasting