The serum levels of IGF-1 are significantly decreased in patients admitted for acute exacerbations of COPD (AECOPD) compared with those in stable stage COPD patients [219, 223, 224] and then increase partly at the time of patients' discharge, but the serum levels of IGF-1 both on admission and on discharge of AECOPD patients are lower than those of healthy controls [223, 224]. Here, IGF1 is linked to chronic obstructive pulmonary disease.