CALCA and rheumatoid arthritis: In our study, the AUC of RF, anti-CCP, and anti-RA33 was 0.66, 0.73, and 0.64, respectively, while with the additions of PCT and CT, the diagnostic ability of early RA was further improved, and the AUC was 0.97, 0.98, and 0.97, respectively (p < 0.01).