GDF15 and sarcopenia: The results of univariate analysis showed that old age (odds ratio [OR]: 1.084, 95% CI: 1.028–1.144, p = 0.003) and elevated serum GDF15 levels (OR: 5.396, 95% CI: 2.313–12.588, p < 0.001) were associated with sarcopenia in patients with COPD.