Previous studies have shown that elevated serum creatinine/cystatin C ratio (CCR) is associated with various diseases, including chronic obstructive pulmonary disease (COPD) (8), DM (9), non-alcoholic fatty liver disease (10), obstructive coronary artery disease (11) and cancer (12, 13) as well as all-cause mortality. This evidence concerns the gene CST3 and chronic obstructive pulmonary disease.