The blood of many persons with RA contains a macroglobulin-type antibody called RF. Evidence indicates that RFs are anti–gamma-globulin antibodies; however, until a specific antigen that produces RF is discovered, the exact nature of RF can only be speculated. Even more uncertain is the role that RF plays in RA. Although RF may cause or perpetuate the destructive changes associated with RA, it may also be incidental to these changes or may even serve some beneficial purpose. RF is sometimes found in blood serum from patients with other diseases, even though RF incidence and values are higher in patients with RA.
This test is useful in the diagnosis of RA. It measures RFs (antibodies directed against the Fc fragment of IgG). These are usually IgM antibodies, but they may also be IgG or IgA.
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions.
Label the specimen with the patient’s name, date, and test(s) ordered and place in a biohazard bag for transport to the laboratory.
When a patient who tests positive improves, subsequent tests also remain positive unless titers were initially low.
A positive RF test result often supports a tentative diagnosis of early-onset RA (e.g., versus rheumatic fever).
RFs frequently occur in a variety of other diseases, such as SLE, endocarditis, tuberculosis, syphilis, sarcoidosis, cancer, viral infections, Sjögren syndrome, and diseases affecting the liver, lung, or kidney as well as in patients who have received skin and renal allografts.
Absence of RF does not exclude the diagnosis or existence of RA.