CHI3L1 and endometriosis: On the other hand, Ural et al. [45] documented that mean serum YKL-40 concentrations were 106.0 ng/mL for the endometriosis group and 52.2 ng/mL for the control group (p = 0.003), which was consistent with the results of YKL-40 concentrations in the endometriosis and control groups we studied.