Medical records about demographic data (age and gender), pulmonary function test (FVC, FEV1, FEV1%FVC, mean expiratory flow (MEF)50), body mass index (BMI), COPD assessment test (CAT), Modified Medical Research Council (mMRC) Dyspnea Scale, and serum PTH, vitamin D, calcium, and phosphate levels were obtained. Here, PTH is linked to chronic obstructive pulmonary disease.