title: [Measurement of rheumatoid factor - diagnostic and prognostic evaluation of patients with arthritis.].
abstract: Measurement of rheumatoid factor (RF) has been used for several decades both for diagnosis and prognostic evaluation of patients with rheumatoid arthritis (RA). The classical way for testing RF is by agglutination, such as the Rose-Waaler and Latex tests. In recent years, however, it has become possible to measure different RF classes by ELISA. About two thirds of routine tests carried out in the Department of Immunology at Landspitalinn in a 10 year period, 1984 to 1993, were performed on patients with diagnosed or suspected rheumatic or autoimmune conditions. RF tests alone were over 30% of all routine tests carried out during this period. In this paper a comparison is made between the information obtained by conventional agglutination tests and class specific RF tests and the literature on the clinical value of RF testing is reviewed. Many studies have showed that measurement of individual RF classes (IgM, IgG and IgA RF) is superior to conventional agglutination tests. Thus, elevation of IgA RF seems to be more specific for RA than a positive agglutination test and IgA RF positive patients have worse prognosis, both regarding the development of bone erosions and extraarticular manifestations, than patients with low IgA RF. Most RA patients have elevation of two or three RF classes, most often both IgM and IgA RF. In contrast, most patients with other rheumatic conditions have elevation of only one RF class, usually IgM RF or IgG RF. Agglutination tests can not discriminate RA patients with elevation of both IgM RF and IgA RF and poor prognosis from those who only have elevation of IgM RF and better prognosis. Furthermore, most patients with an isolated elevation of IgA RF, and poor prognosis, are negative when tested by agglutination only. It is concluded that measurement of individual RF classes give the clinicians earlier and more accurate diagnostic and prognostic information about rheumatic patients.
authors.forename: T
authors.initials: T
authors.lastname: Jonsson
authors.forename: H
authors.initials: H
authors.lastname: Valdimarsson