Many patients ask their doctors in the clinic, “If I have a positive rheumatoid factor, does that mean I have rheumatoid arthritis?” Many non-rheumatologists also often equate a patient with a positive rheumatoid factor with rheumatoid arthritis. This is a misconception. Rheumatoid factor is an autoantibody against the IgG Fc region of immunoglobulin and is therefore an anti-antibody. Positive rheumatoid factor is seen in about 50% of patients with initial rheumatoid arthritis, and in about 20-35% of additional patients during the six months of follow-up. The name “rheumatoid factor” is very reminiscent of rheumatoid arthritis. In fact, a positive rheumatoid factor is not the same as rheumatoid arthritis. For one thing, rheumatoid factor is not specific to rheumatoid arthritis, but can also be seen in many other diseases, especially those that chronically stimulate the immune system over time. Including: 1, other rheumatic immune diseases: dry syndrome, systemic lupus erythematosus, etc. 2, infections: viral infections such as hepatitis C, EBV virus infection, influenza, etc., bacterial infections such as endocarditis, osteomyelitis, tuberculosis, etc. 3, chronic inflammatory state. 4, liver disease, inflammatory bowel disease, etc. Second, normal people also have about 5% rheumatoid factor positive, the elderly have a higher rate of positivity, up to about 10%. Third, strictly speaking rheumatoid factor should not only report positive or negative, but should report titers. Fourth, there are seven diagnostic criteria for the classification of rheumatoid arthritis, and four of them are met in order to be diagnosed. And rheumatoid factor is only one of them. Therefore, rheumatoid arthritis cannot be diagnosed based on a positive rheumatoid factor alone. The rheumatoid factor negative does not necessarily exclude rheumatoid arthritis. Sixth, it is believed that the most specific antibody for the diagnosis of rheumatoid arthritis is the anti-cyclic citrullinated peptide antibody. This antibody has a positive rate of 60-70% in patients with initial diagnosis of rheumatoid arthritis and a specificity of 90-98%. Therefore, a positive rheumatoid factor cannot simply be equated with rheumatoid arthritis.