Rheumatoid Factors in Patients
with Rheumatoid Arthritis

Rheumatoid Factor has a role in the management of patients with Rheumatoid Arthritis, but it is important for Family Physicians to understand just what that role is.

Rheumatoid factors (RF) are antibodies that recognize the Fc portion of an IgG molecule as their antigens. RFs can be of any isotype (IgM, IgG, IgE). Most of the RFs that are measured clinically are the IgM RFs. Rheumatoid Factors probably developed in humans as a mechanism to help remove immune complexes from the circulation.

Many conditions associated with chronic inflammation are also associated with positive RF. (See table) The incidence and titre increase with age. By age 70, up to 14% of individuals are RF positive.

RF is not a screening test for rheumatoid arthritis (RA) in patients with musculoskeletal pain without joint swelling. The predictive value of a test for RA depends on the sensitivity and specificity of the test and the pretest probability of RA. The presence of RF in numerous conditions other than RA limits its specificity. Since RF is not present in all patients with RA, the sensitivity of the test is also reduced. In patients with diffuse musculoskeletal pain without joint swelling, the predictive value of the test is approximately 16%. In patients with a high pretest probability of RA: those with symmetric polyarticular joint swelling, the predictive value of RF factor increases to 80%

In patients with rheumatoid arthritis, RF is an important predictor of a poor prognosis. In high titres it portends increased joint erosion, extraarticular manifestations and greater disability. RFs deposited in tissues are responsible for rheumatoid nodule formation. In RA patients, approximately 70% are RF positive at disease onset and 85 % become positive over the first 2 years. Serum levels of RFs do not change rapidly and cannot be used to follow disease activity.

Some Diseases associated with a Positive Rheumatoid Factor

Rheumatic Diseases
  • Rheumatoid arthritis
  • Sjogren's syndrome
  • Systemic Lupus Erythematosus
  • Mixed Cryoglobulinemia
Bacterial Infections
  • Endocarditis
  • Tuberculosis
  • Syphilis
  • Lyme disease
  • Viral disease
  • AIDS
  • Hepatitis C
  • Infectious mononucleosis
  • Influenza
Lung Diseases
  • Interstitial Fibrosis
  • Silicosis
  • Sarcoidosis
Others
  • Aging
  • Malignancy
  • Periodontal disease

 

- Diane Wilson

Thanks to Dr. Juris Lazovkis, Rheumatologist, at the Cape Breton Regional Health Centre, Sydney, Nova Scotia, for reviewing the draft copy of this article.

References:
  1. Mikkelson WM et al: Estimates of the prevalence of the rheumatic disease in the populations of Tecumseh, Michigan, 1959-60 J. Chron Dis 20:351-369 1967
     
  2. Koopman WJ, Arthritis and Allied Conditions, 14th Edition

You can search for abstracts of the above references by following this link: PubMed

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