Analysis of clinical use of rheumatoid factor

American Family Physician,  March, 1992  

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Rheumatoid factor is an 1gm antibody directed against IgG. Its biologic function is unknown. Rheumatoid factor determination is a test commonly used for diagnostic purposes in patients with musculoskeletal complaints, yet it has significant limitations in sensitivity, specificity and predictive value. Shmerling and Delbanco review the data on rheumatoid factor to identify circumstances in which it has the highest utility and those in which its yield is low.

Although rheumatoid factor may be present in up to 90 percent of patients with rheumatoid arthritis, it is also present in persons with a number of related and unrelated conditions (see tables). Thus, when used as a diagnostic test, false-positive results may occur, leading to possibly unnecessary and inappropriate testing and treatment. In addition, rheumatoid factor may be negative in up to 35 percent of persons who meet other criteria for the diagnosis of rheumatoid arthritis; these falsenegative results may also cause delay in diagnosis and treatment. Rheumatoid factor is not a good screening test in asymptomatic patients since no preventive therapy is available to alter the course of the disease.

Diagnostically, rheumatoid factor is most helpful in patients whose pretest probability of having rheumatoid arthritis is neither very low nor very high. In patients already known to have rheumatoid arthritis, rheumatoid factor is primarily of prognostic value; higher titers are generally associated with more severe disease.

The authors conclude that rheumatoid factor is most useful as a diagnostic test when the patient's pretest probability of rheumatoid arthritis is moderate. In other situations, it has rather limited clinical utility. The authors believe that rheumatoid factor tests are often ordered in clinical situations in which the diagnosis of rheumatoid arthritis is unlikely. More selective use of rheumatoid factor tests could save money and avoid unnecessary delay in diagnosis. (American Journal of Medicine, November 1991, vol. 91, p. 528.)

Rheumatic Diseases Associated
with a Positive Rheumatoid Factor Test
Disease                            Frequency
Rheumatoid arthritis               50-90
Systemic lupus erythematosus       15-35
Sjogren's syndrome                 75-95
Systemic sclerosis                 20-30
Polymyositis/dermatomyositis        5-10
Cryoglobulinemia                   40-100
Mixed connective tissue disease    50-60
Nonrheumatic Conditions Associated
with a Positive Rheumatoid Factor Test
                                          Frequency
Condition                                 (%)
Age over 70 years                         10-25
Primary biliary cirrhosis                 45-70
Malignancy                                5-25
Infection
  Bacterial endocarditis                  25-50
  Liver disease                           15-40
  Tuberculosis                            8
  Syphilis                                Up to 13
  Parasitic diseases                      20-90
  Leprosy                                 5-58
  Viral infection                         15-65
Pulmonary disease
  Sarcoidosis                             3-33
  Interstitial pulmonary fibrosis         10-50
  Silicosis                               30-50
  Asbestosis                              30

COPYRIGHT 1992 American Academy of Family Physicians
COPYRIGHT 2008 Gale, Cengage Learning