Britannica Sources used in this answer

What does rheumatoid factor indicate in rheumatoid arthritis testing?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Know about prosthetic jaw joint replacement and how that technology can help in other joint replacements like the shoulder, the hip, or even the spine — arthritis Learn about prosthetic jaw joint replacements and how that technology can be used for hip, shoulder, and spinal joint replacements.

In the context of rheumatoid arthritis, rheumatoid factor refers to a group of autoantibodies—most notably immunoglobulin M (IgM) antibodies—that react against IgG immunoglobulins.1

When used in testing, rheumatoid factor serves as a key indicator of an autoimmune mechanism, where the immune system inappropriately attacks the body's own tissues. Its presence is a significant diagnostic feature, found in approximately 70 to 80 percent of individuals with the disease. Furthermore, serum levels of rheumatoid factor are directly related to both the severity of the disease and the likelihood of experiencing extra-articular manifestations.12

However, it is important to note that rheumatoid factor cannot be used as a standalone diagnostic tool. Because elevated levels can be associated with various other conditions, clinicians use the rheumatoid factor test in conjunction with other blood tests—such as those for antinuclear antibodies or C-reactive protein—and clinical evaluations to confirm a diagnosis.21