GDF15 and chronic obstructive pulmonary disease: In humans, the circulating concentrations of GDF‐15 that we observed in COPD patients were lower than those seen in some studies of colon and metastatic prostate cancer where serum GDF‐15 levels can exceed 100 ng/mL.37 These lower levels of GDF‐15 may also account for the apparent lack of association of GDF‐15 with BMI.