GDF15 and Hyperglycemia: The increase in circulating GDF-15 in patients with ICUAW, which is consistent with our previous study,9 is likely to be a result of critical illness because factors thought to contribute to ICUAW, including hyperglycaemia, inflammation and oxidative stress,2, 4 stimulate GDF-15 expression in other tissues6, 24 and, therefore, may drive the observed increase in GDF-15 expression in ICUAW muscle.