Many primary care physicians treating patients with arthralgia always recommend that the patient get an RF (rheumatoid factor) test, and once the RF is positive, the patient is diagnosed with rheumatoid arthritis. In fact, RF is not a strong indicator for diagnosing rheumatoid arthritis specifically, and many diseases can be positive for RF, so we cannot say that a positive RF is rheumatoid off. Therefore, clinically for patients with arthralgia, we need to properly evaluate and recognize RF, and we should also carefully joint examination, take medical history, and combine with other experimental indicators (such as CCP, antiperinuclear factor, anti-keratin antibody and imaging indicators, etc.). RF refers to specific antibodies against the antigenic determinants of the Fc segment of the human or animal IgG molecule and is one of the criteria for the diagnosis of RA, but not the only one. Generally speaking, RF positivity can be seen in the following conditions or diseases. 1, normal people, about 2-5% of normal people can appear RF positive, and with the age of RF positive rate can increase, the elderly RF positive rate is higher; 2, rheumatoid arthritis, high titer RF indicates rheumatoid arthritis disease serious, poor prognosis; 3, other rheumatic immune diseases, prominent representatives of dry syndrome (its RF frequency and titer is not lower than rheumatoid off), and lupus erythematosus, scleroderma, mixed connective tissue disease, polymyositis/dermatomyositis and other rheumatic diseases; 4, infectious diseases: mononucleosis, parasitic infections, chronic viral infections, chronic bacterial infections (tuberculosis), etc.; 5, chronic diseases: especially liver and lung diseases, such as cirrhosis, chronic active hepatitis, diffuse interstitial lung fibrosis, nodular disease, macroglobulinemia, etc., and tumors . Therefore, a positive RF does not mean rheumatoid arthritis. In clinical practice, for patients with arthralgia, even if the rheumatoid factor is positive, we must take a careful medical history and examine the joints carefully (arthralgias, small joint lesions on the hands, multiple joint areas, with significant morning stiffness, the diagnosis of rheumatoid arthritis is of great value), combined with other antibodies (such as CCP, anti perinuclear factor, anti-keratin antibodies, etc., if both are positive, the diagnosis of rheumatoid arthritis is of great value). The diagnosis of rheumatoid arthritis can be made by combining other antibodies (e.g. CCP, anti perinuclear factor, anti-keratin antibodies, etc., if both are positive, the diagnosis of rheumatoid arthritis is even more valuable) and, if necessary, by referring to MRI of the diseased joints (e.g. wrist joints). The diagnosis of rheumatoid arthritis should not be based solely on a positive rheumatoid factor.