Objective: . To compare the diagnostic value of anti-cyclic citrullinated peptide (anti-CCP) and anti-Sa antibodies in serum for prediction of rheumatoid arthritis (RA) in an outpatient clinic for connective tissue diseases and spondyloarthritides.
Methods: A cross-sectional study was carried out to analyze the presence or absence of anti-CCP and anti-Sa antibodies in the sera of 250 randomly selected patients. The disease distribution in the study was as follows: 87 patients had RA (34.8%); 90 (36%) had other connective tissue diseases (CTD); 50 (20%) spondyloarthritis; 19 (7.6%) polymyalgia rheumatica; and 4 (1.6%) juvenile idiopathic arthritis.
Results: Anti-CCP antibodies were detected in 63 patients with RA and in 9 patients with other illnesses [sensitivity 72.4%, specificity 94.4%, positive predictive value (PPV) 87.5%]. Anti-Sa antibodies were detected in 38 patients with RA and in 6 patients with other illnesses (sensitivity 43.6%, specificity 96.3%, PPV 86.3%). Anti-CCP and anti-Sa results were discordant in up to 47 of 87 RA patients. No relation between the presence of anti-Sa and higher or lower titers of anti-CCP antibodies was observed.
Conclusion: The diagnostic value in RA is similar for both antibodies. However, the sensitivity of anti-CCP detection is higher than that of anti-Sa. Our results suggest that presence of anti-Sa antibodies in serum may be useful as a complementary assay when anti-CCP antibodies are negative and RA is suspected.