Clinically, serum CHI3L1 was measured by chemiluminescence immunoassay (CLIA) in RA patients (n=102) and controls (n=79), stratified by 28-joint Disease Activity Score with erythrocyte sedimentation rate (DAS28-ESR), and correlated with C-reactive protein (CRP), rheumatoid factor (RF), anti-cyclic citrullinated peptide antibody (CCP), and ESR. Here, CRP is linked to rheumatoid arthritis.