Rheumatoid Factor (RF)

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Subject: Rheumatoid Factor (RF)

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Definition

  • RF is an immunoglobulin present in the serum of 50–95% of adults with RA. It appears in serum and synovial fluid several months after onset of RA and is present up to years after therapy. The autoantibodies are usually of IgM class, although approximately 15% of RA has IgG class. Most methods detect only the IgM class.

  • Normal range: <20 IU/mL.

Use

  • Assisting in the diagnosis of RA, especially when clinical diagnosis is difficult

Interpretation

Increased In

  • Chronic hepatitis

  • Chronic viral infections

  • Cirrhosis

  • Dermatomyositis

  • Infectious mononucleosis

  • Leishmaniasis

  • Leprosy

  • Malaria

  • RA

  • Sarcoidosis

  • Scleroderma

  • Sjögren syndrome

  • SLE

  • Syphilis

  • TB

  • Waldenström macroglobulinemia

Limitations

  • RF is not a finding isolated to RA and may be present in a number of connective tissue and inflammatory diseases, including infectious mononucleosis, SLE, scleroderma, and hepatitis.

  • Older patients may have higher values.

  • Recent blood transfusion, multiple vaccinations or transfusions, or an inadequately activated complement may affect results.

  • Serum with cryoglobulin or high lipid levels may cause false-positive test results.

 
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