CHI3L1 and idiopathic pulmonary fibrosis: Baseline serum CHIT1 activity and YKL-40 concentration had a similar discriminatory ability to differentiate patients with IPF from controls (AUC value of 0.806; p=0.00001 for CHIT1 and AUC value 0.788; p=0.0001 for YKL-40).