Type of test Blood
Normal findings
Negative (< 60 units/mL by nephelometric testing)
(Elderly patients may have slightly increased values.)
Test explanation and related physiology
In rheumatoid arthritis (RA), abnormal immunoglobulin G (IgG) antibodies produced by lymphocytes in the synovial mem branes act as antigens. Other IgG and IgM antibodies in the patient’s serum react with the fc component of the abnormal synovial antigenic IgG to produce immune complexes. These immune complexes activate the complement system and other inflammatory systems to cause joint damage. The reactive IgM is called RF. Tissues other than the joints, including those of the blood vessels, lungs, nerves, and heart, may also be involved in the autoimmune inflammation.
Tests for RF are directed toward identification of the IgM antibodies. Approximately 80% of patients with RA have positive RF titers. To be considered positive, RF must be found in a dilution of greater than 1:80; when RF is found in titers less than 1:80, such diseases as systemic lupus erythematosus, scleroderma, and other autoimmune conditions should be considered. Although the normal value is “no rheumatoid factor identifiable at low titers,” a small number of normal patients will have RF present at a very low titer. Furthermore, a negative RF does not exclude the diagnosis of RA. RF is not a useful disease marker because its presence does not disappear in patients who are experiencing a remission from the disease symptoms.
Other autoimmune diseases such as systemic lupus erythematosus and Sjögren syndrome also may cause a positive RF test. RF is occasionally seen in patients with tuberculosis, chronic hepatitis, infectious mononucleosis, and subacute bacterial endocarditis as well.
Interfering factors
• Elderly patients often have false-positive results.
• Hemolysis or lipemia may be associated with false-positive results.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red
Abnormal findings
Increased levels
- RA
- Other autoimmune diseases (e.g., systemic lupus erythematosus)
- Chronic viral infection
- Subacute bacterial endocarditis
- Tuberculosis
- Chronic hepatitis
- Dermatomyositis
- Scleroderma Infectious mononucleosis
- Leukemia
- Cirrhosis
- Syphilis
- Renal disease
