The optimal cut-off values according to the Youden index for YKL-40, YKL-39, and SI-CLP to differentiate RA responders from non-responders to csDMARDs were 1.38 ng/mL, 3.26 ng/mL, and 4.10 ng/mL, respectively. This evidence concerns the gene CHI3L1 and rheumatoid arthritis.