Antiperinuclear factor in an Italian series of patients with rheumatoid arthritis

Serum samples from 90 cases of rheumatoid arthritis (RA), 218 control patients and 100 healthy controls were tested by indirect immunofluorescence for the presence of the antiperinuclear factor (APF), an autoantibody to the keratohyaline granules of human buccal mucosal cells. The sensitivity and specificity of the APF test for RA were 82 and 90%, respectively, slightly higher than those obtained when the same serum samples were tested for rheumatoid factor (RF) using a latex agglutination method. The diagnostic gain of APF in the RF-negative RA cases was greater than that of RF in the APF-negative cases (54% vs. 37%). In spite of a few technical disadvantages, the APF test should be therefore performed in the serological routine examination of rheumatic diseases. As APF was also found in 11% of degenerative joint disease (DJD) cases and the estimated prevalence ratio RA/DJD is, in Italy, 1/11, the predictive value of a negative APF test proved to be much higher than that of a positive test (98% vs. 40%) for the diagnosis of RA. APF was significantly associated with other autoantibodies (RF and antinuclear antibody).