Clinical significance:

Rheumatoid factor is an antiglobulin antibody directed against human and animal immunoglobulin G epitopes. The most common, 80%, is the classic RF factor (RF IgM) discovered in 1949 by Waaler and Rose.

Rheumatoid Factor (RF IgM)

Other than this, rheumatoid factors can belong to immunoglobulin class G or A, less commonly D or E. Rheumatoid factor is the mainserological marker in the diagnosis of rheumatoid arthritisrzs (85%) and in patients with other connective tissue diseases (Sjögren's syndrome, systemic lupus erythematosus, systemic scleroderma, mixed connective tissue disease and others). In low titers, it is also detected in about 3-5% of healthy individualsb especially after 60 years of age.

In rzs, in addition to stimulating the immune system and forming immune complexes, RF is involved in complement activation. RF combined with immune complexes intensifies inflammatory processes leading to cartilage destruction and joint destruction, as well as the development of extra-articular form of rzs (cardiovascular, respiratory, ocular, renal lesions, rheumatoid nodules).

Seropositive RF is also involved in the development of the immune complexes

Seropositive form of rzs is usually characterized by a more severe course of the disease. The presence of RF IgG may be associated with the occurrence of vasculitis in rzs, while RF IgA is considered a marker of the erosive form and increased bone erosive changes. Determination of RF in immunoglobulin classes other than IgM is only of ancillary importance. Rheumatoid factor levels also fluctuate depending on the active disease process, which is useful in monitoring the course of the disease and the effectiveness of treatment.

RF is routinely determined by classical Waaler-Rose and latex reagents (qualitative result) or by immunoturbidimetry, nephelometry or ELISA methods (quantitative result). Rheumatoid factor can be determined in serum, as well as in joint fluid and effusion fluids.