ANTIPERINUCLEAR FACTOR - A USEFUL TEST FOR THE DIAGNOSIS OF RHEUMATOID-ARTHRITIS

The objective of this study was to determine: (1) the diagnostic value of antiperinuclear factor (APF), (2) the types of immunoglobulins inv olved in the reaction and (3) the presence of the antibody in paired s amples of serum and synovial fluid (SF). We studied 408 serum samples from the following: healthy controls (12=68), patients with rheumatoid arthritis RA; n = 160, 106 RF-positive and 54 RF-negative and patient s with other rheumatic diseases (n = 180). We examined paired serum an d SF samples in 27 patients (8 with RA and 19 with other rheumatic con ditions). APF was determined by an indirect immunofluorescence assay. A group of 30 APF-positive serum samples was incubated with fluorescen t-labelled antisera against IgG, IgM and IgA independently. APF was po sitive in 55.7% of patients with RF-positive RA, in 35.2% of patients with RF-negative RA, in 11.1% of patients with other rheumatic disease s and in 5.9% of healthy controls. Statistical differences were found between RF-positive RA and the other three groups (P = 0.02, P = 0.000 1, P = 0.0001, respectively) and between RF-negative RA and the groups of other rheumatic diseases (P = 0.0001) and healthy controls (P=0.00 5). The specificity of the test for RA was 90.2%. APF was present in t hree SF samples from RA patients (37.5%). The reaction was mediated by immunoglobulins of the IgG class in 100% of those tested, and, in add ition, 30% were of IgA and 6.7% of IgM classes. We concluded that APF is a good diagnostic test that could be included in the classification criteria of RA, it can be present in SF and it is predominantly an an tibody of the IgG class.