To assess the diagnostic and prognostic power of antiperinuclear factor (APF) and to identify a specific pattern of rheumatoid arthritis (RA) of different evolution and prognosis.
One hundred and fifty-nine sera from patients with RA, 280 sera from patients with other rheumatic diseases and 204 sera from healthy subjects were examined for APF.
Sensitivity and specificity of the test were, respectively, 0.82 and 0.99 when 1:80 serum dilution was considered positive but 0.84 and 0.92 when tested at the currently used 1:5 serum dilution. According to the data obtained from APF and rheumatoid factor (RF) testing, patients with RA were subdivided in 4 groups. Clinical and demographic features for each group were analyzed. RF+ and/or APF+ patients showed a common pattern of disease, whereas RF-/APF- patients showed fewer extraarticular manifestations (p < 0.02) including Sjögren's syndrome (p < 0.04) and an unusual onset of the disease characterized by an involvement of large joints (p < 0.0001). Higher titer of APF was detected at the onset of the disease than in longstanding RA (p < 0.02).
APF is a valuable diagnostic tool and a useful additional marker for RA. 1:80 serum dilution allows more specificity without substantial loss of sensitivity. A specific pattern of RA can be identified on the basis of APF status.