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Autoimmune Screen

Rheumatoid Factor

September 12th, 2020


Rheumatoid factor is a heterogeneous group of immunoglobulins against antigens classically found to be present in rheumatoid arthritis.
    • Normal Range

    • <20 U/mL
  • Causes of Elevated Rheumatoid Factor

  • Physiologic - elevated in 15% of normal people
  • Inflammatory disease - rheumatoid arthritis, Sjögren's, SLE, sarcoidosis, pulmonary fibrosis, cryoglobulinaemia
  • Bacterial infection - subacute bacterial endocarditis, TB, syphilis
  • Viral infection - hepatitis C, EBV, CMV, HIV, rubella
  • Parasitic infection - malaria, toxoplasmosis, Chagas disease
  • Cirrhosis
  • Malignancy
  • Pearls

  • Rheumatoid factor is classically used as a marker of rheumatoid arthritis, with 70% sensitivity and 70% specificity - therefore a positive test does not confirm RA and a negative test does not rule out RA
  • The test is generally interpreted with anti-CCP antibodies as the two tests together are more predictive
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