"Rheumatoid Factor IgM is an ELISA test system for the quantitative measurement of IgM class rheumatoid factor in human serum or plasma samples. The test is used as an aid in the differential diagnosis of rheumatoid arthritis (RA), and presence of rheumatoid factors (RF) is an integral part of the current ACR criteria for classification of RA. In established RA, high titres of serum IgG and especially IgM RF indicate poor prognosis. The presence of either IgG or IgA RF in patients with long-standing RA may be a prognostic indicator of systemic manifestations. Evaluation of a test result should always take into account all clinical and laboratory findings."