CHI3L1 and obstructive sleep apnea syndrome: Serum OPG (Area Under the Curve (AUC) = 0.7771, p < 0.0001, a cut-off value of <47.78 pg/mL), serum YKL-40 (AUC = 0.9734, p < 0.0001, cut-off value of >3759 pg/mL), serum CT-1 (AUC = 0.8749, p < 0.0001, cut-off value of >3805 pg/mL), plasma OPG (AUC = 0.8126, p < 0.0001, a cut-off value of <37.56 pg/mL), plasma YKL-40 (AUC = 0.9210, p < 0.0001, cut-off value of >3343 pg/mL), and plasma CT-1 (AUC = 0.8273, p < 0.0001, cut-off value of >1749 pg/mL) present high sensitivity and specificity in predicting the presence of moderate and severe OSA (AHI ≥ 15) (Figure 1 and Figure 2).