Rheumatoid factor (RF) was first identified by Rose (1948) in the sera of patients with rheumatoid arthritis (RA) as an autoantibody targeting the Fc segment of denatured IgG. RF-producing B-cell clones are present in RA patients and in about 5% of healthy individuals, and RF can be synthesized in large quantities under the direct action of denatured IgG (IgG bound to antigen) or EBV. In healthy individuals, there are fewer RF-producing cell clones, and soluble factors secreted by monocytes can inhibit RF production, so it is generally not easily measured. RF is contained in a variety of immunoglobulins and reacts with IgG molecules from a variety of animals to bind with its Fc segment and neighboring Fc segments, RF has five categories: IgG, IgA, IgM, IgE, IgD, IgG-RF can bind itself to form a dimer, this dimer and two normal IgG molecules to form an intermediate complex associated with vasculitis in RA patients, in synovial IgGRF dimer in the synovial fluid can further form multimers deposited on the cartilage surface, activating complement and causing damage to the joint, which cannot be measured by indirect agglutination because it is a dimer. What we now measure by latex agglutination test is IgM-like RF, IgM-RF is pentameric and can bind to the Fc segment of five latex particle-coated IgG molecules to form large laminar deposits, so it can be observed with the naked eye. Latex agglutination method to measure RF: Reagents: 1, rheumatoid factor latex 2, saline Main equipment: 1, U-shaped round bottom 72-well dilution plate 2, 25 dilution rod 3, oscillator Method: 1, in the dilution plate with saline, the first, 2 holes 75l, the 3rd, 4th, 5th, 6 holes 25l 2.Dilution stick with patient serum (25l) first placed in the first well, mixed 30-50 times, moved out to the second well, and so on. 3.After mixing, add no latex to the first well, double the latex to the second well, and add a drop to the 3rd, 4th, 5th and 6th wells. Shake well on the shaker for about 3-5 minutes, place it in the refrigerator at 4 degrees overnight, and take it out for one hour the next day to observe the results. Results: The presence of agglutination reaction is positive, and the titer is reported to whichever well the agglutination is to. Now there is a biochemical instrument available turbidimetric method to detect RF, its positive rate and latex agglutination method is basically the same, this method is also measured IgM-RF. In addition, the double antigen sandwich ELISA method can also detect IgG, IgA, IgD-RF. heat polymerization of human or rabbit IgG as antigen-coated enzyme standard plate, plus a certain dilution of human serum, the reaction is added to the most appropriate dilution of HRD (spicy After the reaction, the most appropriate dilution of HRD (spicy peroxidase) labeled thermopolymerized IgG was added, and the substrate was added after a certain time, and then the absorbance at 492 nm was measured. The clinical significance of RF measurement: RF in rheumatoid arthritis positive rate of about 80%, is one of the important serological criteria for the diagnosis of RA, but not the only criterion, because 5% of the normal voluntary RF can be positive, with age, the positive rate can increase, other autoimmune diseases such as dry syndrome, systemic lupus erythematosus, scleroderma, polymyositis, and infectious diseases such as hepatitis, tuberculosis, non infectious diseases such as diffuse interstitial lung fibrosis, liver cirrhosis, and nodular disease can be seen. Persistent high titers of RF are common in the active phase of RA disease and have a high incidence of bone erosion.