RETN and chronic obstructive pulmonary disease: Age (OR: 1.107, 95% CI: 1.007–1.217, P = 0.036), BMI (OR: 1.284, 95% CI: 1.074–1.536, P = 0.006), serum resistin level (OR: 1.001, 95% CI: 1.000-1.001, P < 0.001), and serum TNF-α level (OR: 1.818, 95% CI: 1.041–3.177, P = 0.036) were associated with SO in patients with COPD in univariate analysis.