COPD patients who have received systemic glucocorticoid exceeding the equivalent of 180 mg prednisolone which are homo / heterozygous for the BclI and / or N363S polymorphisms (associated with increased glucocorticoid sensitivity) will have a lower cortisol response in a synacthen® test (greater suppression of adrenal corticosteroid) than the corresponding patients there are wild-type or homo- or heterozygous for the polymorphic ER22 / 23EK and / or 9β (associated with decreased sensitivity). Information from the results of the investigation will be able to help clinicians to identify patients with acute exacerbation of COPD (AECOPD) at risk of of secondary adrenal insufficiency.