MUC1 and chronic obstructive pulmonary disease: The mean induced sputum level of KL-6 was higher in patients with COPD than in the middle aged/elderly smokers without COPD; 203 ± 41 U/ml vs 96 ± 22 U/ml, p = 0.002), the corresponding value in the middle aged/elderly non-smokers being 68 ± 20 U/ml, p = 0.033).