CHI3L1 and chronic obstructive pulmonary disease: Very recently, Matsuura conducted similar measurements in 12 non-smokers, 11 (presumably current) smokers without COPD and 18 (presumably current) smokers with COPD [27]; both studies indicated that the serum levels of YKL-40 in smokers with COPD were significantly higher than those in smokers without COPD, or in non-smokers.