An antibody that is present eventually in most people with rheumatoid arthritis (RA). RA is an inflammatory condition in which the immune system, which normally protects the body from bacteria and other invading organisms, mistakenly launches an attack on the synovial membrane of joints. This attack in turn causes pain, swelling, stiffness, and loss of function in the joints. RA can also affect other tissues, including skin, lungs, kidneys, eyes, and blood vessels.
RA can be difficult to diagnose in its early stages. The symptoms vary from person to person, can be more severe in some patients than in others, and are similar to those of other types of arthritis and joint conditions.
Rheumatoid factor (RF) is an antibody, a special protein made by the immune system to attack foreign substances. Doctors use a test for RF to help diagnose RA. Not everyone with RA tests positive for RF, and some people test positive for RF without ever developing RA. Furthermore, people with other conditions such as systemic lupus erythematosus, Sjogren’s syndrome, or certain liver diseases may test positive for RF. Nonetheless, a positive RF test can help confirm RA in people who have typical RA symptoms. The test is also helpful in that higher levels of RF are associated with more severe cases of RA.