Comparison of anti-CCP titers in Sa+ and Sa- patients. To investigate a possible relationship between anti-Sa and anti-CCP autoantibodies, we compared anti-CCP2 antibody titers in 46 anti-Sa-positive rheumatoid arthritis (RA) sera, 15 anti-Sa-negative RA sera, and 26 control sera, using the CCP2 test kit. Ninety-six percent of anti-Sa-positive RA patients, 60% of Sa-negative RA-patients, and none of the control patients was positive for anti-CCP2. Anti-Sa-positive RA sera had a significantly higher anti-CCP titer (852 ± 96 U; mean ± SEM) than anti-SA-negative sera (263 ± 110 U) (P < 0.0005; Mann–Whitney test). None of the control sera tested positive in either of the two assays (12 ± 0.4 U).