Special laboratory tests that make the diagnosis of inflammatory polyarthritis more likely are tests for antibodies against cyclic citrullinated peptides and for IgM rheumatoid factors. IgM rheumatoid factors (RF) are found in about 65–80% of patients with rheumatoid arthritis (RA), but also in other rheumatic diseases and in up to 5% of healthy people.
Antibodies against citrullinated peptides/proteins (ACPA) include antibodies against cyclic citrulline (CCP), against mutated (MCV) and non-mutated (Sa) citrullinated vimentin, and against citrullinated fibrinogen.
Anti-CCP antibodies can be detected years before rheumatoid arthritis becomes clinically apparent, and in undifferentiated arthritis they have a high predictive value for the development of rheumatoid arthritis.
Testing for other autoantibodies (e.g. ANA) mainly serves to detect or rule out other rheumatic diseases that can sometimes look similar clinically (e.g. connective tissue diseases).
ANA testing is carried out in our own laboratory, among other methods by indirect immunofluorescence, in which different types of antibodies show typical patterns.