To explore the relationship between serum osteoprotegerin (OPG) and the diagnosis of bone loss and osteoporosis in patients with chronic obstructive pulmonary disease (COPD).

From January 2021 to March 2024, ninety-five COPD patients with stable disease were recruited from Our hospital, and were divided into the normal bone mineral density (BMD) group (n=35), the reduced BMD group (n=37), and the osteoporosis group (n=23) according to the dual-energy X-ray absorptiometry (DEXA), and enzyme-linked immunosorbent assay (ELISA) was used to determine the serum OPG levels.

Body mass index (BMI) and forceful lung capacity (FVC) were higher in the BMD normal group than in the BMD reduced and osteoporotic patients (P<0.05). Glycosylated hemoglobin (HbA1c) was lower in osteoporotic patients than in the BMD normal and reduced BMD groups, in addition to lower force expiratory volume in 1 second (FEV₁) than in the BMD normal group (P<0.05). As BMD decreased, lumbar spine BMD and T scores as well as hip BMD and T scores gradually decreased (P<0.001); while serum OPG levels gradually increased (F=23.257, P<0.001). Serum OPG levels were significantly lower in patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification 1-2 than in patients with GOLD classification 3-4 (t=-3.332, P=0.001). Spearman′s correlation showed a weak negative correlation between serum OPG levels and FEV₁(Rho=-0.205, P=0.046), FEV₁/FVC (Rho=-0.236, P=0.022), and FEV_{25_75} (Rho=-0.226, P=0.028). The above BMI, HbA1c, FVC, FEV₁, and OPG were included as independent variables in the multiple linear regression equation, and the results showed that BMI, HbA1c, and serum OPG were independently correlated with lumbar spine T-scores (P<0.05); whereas, BMI and serum OPG were also independently correlated with hip T-scores (P<0.05). The BMD normal group was used as a control, and serum OPG diagnosed decreased BMD with an AUC was 0.737(95%CI: 0.617~0.857), and the cutoff value was 187.01 pg/ml; with the patients with normal BMD and reduced BMD as the control, the AUC of serum OPG for diagnosing osteoporosis was 0.825 (95%CI: 0.741~0.909), and the cutoff value was 206.39 pg/ml; with the reduced BMD group as a control, the AUC of serum OPG for diagnosis of BMD reduction was 0.683 (95%CI: 0.550~0.815), and the cutoff value was 187.01 pg/ml; all P<0.05.

High serum OPG levels are associated with the risk of osteoporosis in COPD patients, therefore OPG may be a biomarker for this COPD related comorbidity.