GDF15 and sarcopenia: In previous studies, we and others have identified biomarkers such as growth differentiation factor 15 (GDF15) [30] and lipoprotein‐associated phospholipase A2 (Lp‐PLA2) [31] as predictors of sarcopenia in patients with COPD, with reported AUCs of approximately 0.827 and 0.744, respectively.