Rheumatoid factor
Rheumatoid factor ( RF) is a building block in the diagnosis of many rheumatic and non- rheumatic diseases. It is in the blood, usually in the serum determined. When rheumatoid factor is autoantibodies of various subclasses (IgM, IgG, IgA, IgE ) directed against specific areas of the body's class G immunoglobulins (IgG) directed ( against the Fc fragment of IgG). The term is often used in the plural (ie " rheumatoid factors ").
A positive rheumatoid factor makes a rheumatic disease more likely, they can not demonstrate. Also makes a negative rheumatoid factor rheumatism Although unlikely, but does not exclude it. One speaks of a " seronegative rheumatoid arthritis " when, although the disease, " rheumatism" (rheumatoid arthritis ) is present, the rheumatoid factor, however, is not detectable. Rheumatoid factors are found in low concentrations even at about 5 % of healthy people (10% in people over 60 years ), Sjögren's syndrome and other connective tissue diseases, liver disease ( including hepatitis C ) or chronic infectious diseases.
A significant improvement of laboratory diagnosis of rheumatoid arthritis has brought the discovery of citrullinated antigens and the antibodies against citrullinated Peptid-/Protein-Antigene ( ACPA ) and their significance for the diagnosis of rheumatoid arthritis. These natural antigens are found within the inflamed synovial tissue and as circulating antigens in the synovial fluid of patients with established rheumatoid arthritis, the antibodies are considered to be so-called biomarkers for rheumatoid arthritis.
The most common here is an ELISA lab test that detects artificial cyclic citrullinated peptides. This evidence of so-called anti -CCP antibodies has led to a significant improvement in the laboratory diagnosis of rheumatoid arthritis, including the diagnosis of early stages of the disease. Antibodies against citrullinated peptides can potentially be detected years before the onset of the disease. A pathogenic role has been demonstrated for CCP antibodies but not so far. The correlation between the anti -CCP antibody titer and disease activity of rheumatoid arthritis is unproven. The CCP antibodies are therefore not suitable as a follow-up parameters of the disease.
An anti- CCP ELISA comparatively good diagnostic sensitivity at a slightly lower specificity provides a novel ELISA based on the mutated citrullinated vimentin, MCV. Initial studies with this test system show the relationship of the anti-MCV antibody titers with disease activity and severity of rheumatoid arthritis. This would allow the anti- MCV antibodies against the anti - CCP antibodies have the advantage of a correlation with disease activity and possibly are also suitable for monitoring of therapy progression in rheumatoid arthritis. For a final evaluation, however, more results from other independent study should be awaited.