This test detects and measures rheumatoid factor (RF), a type of “autoantibody”, in the blood. We all have antibodies (also known as immunoglobulins) in our blood, which are protective proteins which defend the body against infection, particularly from bacteria. However, “autoantibodies” may attack the patient’s own tissues mistakenly identifying them as “foreign”. While the role of RF is not well understood, it may not directly cause joint damage, but promote the body’s inflammation reaction which in turn contributes to autoimmune joint destruction.
The RF test is sensitive but not very specific, it can be found in diseases other than rheumatoid arthritis (RA). It is most closely associated with RA but may also be present in other autoimmune disorders, such as Sjögren’s syndrome, in some persistent bacterial and viral infections, and can be found in a small but significant percentage of healthy people particularly in the elderly.