The relationship between annual lung function decline and serum bilirubin levels in chronic obstructive pulmonary disease

Aim: To investigate the relationship between serum bilirubin levels and annual decline in lung function in patients with chronic obstructive pulmonary disease (COPD). Materials and Methods: In this retrospective study, medical records of 1,574 patients diagnosed with COPD were screened. A total of 126 patients who met the inclusion criteria were included in the study. Data from the initial visits and pulmonary function tests performed at the end of the first year, along with serum direct bilirubin and total bilirubin (TB) measurements, were obtained from the electronic system and analyzed. The Pearson correlation test was used to determine the relationship between two continuous variables. Results: A statistically significant negative correlation was found between the mean TB values and the annual changes in predicted forced expiratory volume in the first second (FEV1) percentage, FEV1 ml, predicted forced vital capacity (FVC) percentage, FVC ml, and predicted forced expiratory flow (FEF)25–75% percentage (r: -0.202, -0.342, -0.236, -0.287, and -0.136, respectively). However, TB values did not have a significant relationship with the change in the FEV1/FVC ratio. Conclusion: The progression speed of COPD may vary among different patients. An elevated serum TB concentration within physiological limits could be considered a parameter that may slow the progression of COPD.