What does rheumatoid factor indicate?

Rheumatoid factor (RF) is an autoantibody that is often associated with rheumatoid arthritis (RA), an autoimmune disease that causes inflammation of the joints. The presence of RF in the blood can be an indication of RA, but it is not always definitive as it can also be found in other conditions such as lupus, Sjögren's syndrome, and infectious diseases.

RF is produced by the immune system and is directed against the body's own immunoglobulin G (IgG) antibodies. When RF binds to IgG, it can form immune complexes that can deposit in the joints and cause inflammation. The presence of RF can indicate that the immune system is attacking its own tissues, which is a characteristic feature of autoimmune diseases.

RF is commonly detected through a blood test called a rheumatoid factor test. This test measures the levels of RF in the blood and can help in the diagnosis of RA and monitoring the disease activity. However, it's important to note that a positive RF test does not always mean that a person has RA, as it can also be present in individuals without the disease. Therefore, a combination of clinical symptoms, other laboratory findings, and imaging studies are typically used to make a definitive diagnosis of RA.