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Rheumatoid factor in the blood
Last reviewed: 04.07.2025
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Reference values (norm) for the concentration of rheumatoid factor in blood serum when determined by nephelometry are less than 14 IU/ml.
Rheumatoid factor is an autoantibody of the IgG, IgM, IgA or IgE classes that reacts with the Fc fragment of IgG. It is formed as a result of stimulation with aggregated modified IgG or due to the effect of an exogenous cross-reacting antigen in case of impaired immunoregulation. The IgG + rheumatoid factor complex is not phagocytosed, it is deposited in the perivascular space, stimulating cell-mediated cytotoxic reactions, which leads to inflammation.
An increase in the concentration of rheumatoid factor in the blood is characteristic of rheumatoid arthritis (up to 90% of patients); no dependence of the rheumatoid factor titer on the duration of the disease has been revealed. Detection of rheumatoid factor in the presence of an appropriate clinical picture confirms the diagnosis of rheumatoid arthritis, but its seronegative forms are possible. An increase in the rheumatoid factor titer is determined no earlier than 6-8 weeks after clinical manifestations. A negative test result does not always allow excluding the diagnosis. The presence of rheumatoid factor in patients with an established diagnosis of rheumatoid arthritis indicates a severe form of the disease (occurs with a pronounced inflammatory process in the joints, often with their destruction). Rheumatoid factor can be detected in low titers in infectious mononucleosis, acute inflammatory processes, systemic lupus erythematosus with joint damage, Sjogren's syndrome, sarcoidosis, and hepatitis.
An increase in the concentration of rheumatoid factor is possible in Felty's syndrome - a special form of rheumatoid arthritis characterized by leukopenia and an acute onset; in Still's syndrome (the test is positive in 20% of cases of the disease) - a juvenile form of rheumatoid arthritis, which clinically occurs like Felty's syndrome, but, unlike it, is accompanied by leukocytosis.
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