ITIH3 and rheumatoid arthritis: In summary, Con A-bound ITIH3 in serum was identified as a robust diagnostic biomarker enabling discriminating RA-sSS from both HC and from pSS and RA alone. The performance of antibody isotypes against citrullinated peptides was generally better than their non-citrullinated/native counterparts, in discriminating between pSS, RA and RA-sSS and, healthy controls.