APBB1 and rheumatoid arthritis: Five autoantibodies showed sensitivity more than 20% and specificity more than 85% in ACPA‐negative RA (n = 48; Table 2), including anti‐ANAPC15 (NM_014042, sensitivity 20.8%, specificity 91.5%), anti‐lymphocyte‐specific protein 1 (LSP1) (BC001785.1, sensitivity 20.8%, specificity 88.9%), anti‐APBB1 (NM_145689, sensitivity 27.1%, specificity 87.7%), anti‐parathymosin (anti‐PTMS, NM_002824, sensitivity 25.0%, specificity 87.7%), and anti‐UBL7 (NM_032907, sensitivity 22.9%, specificity 87.3%).