Problems in Interpretation of the short ACTH test: an update and historical notes

ACTH stimulation test has been used for many years. Some important questions remain unsettled. These are reviewed and discussed in detail. Interpretation of a short ACTH test rests on the fact that a close correlation exists between the responses in plasma cortisol concentrations after administration of ACTH and during insulin induced hypoglycaemia which previously was the standard test. It is generally assumed that the plasma cortisol concentration after ACTH (and insulin) mirrors the response in major stress situations (surgery and critical disease). This notion rests on few observations. Furthermore, extensive changes in protein binding of cortisol occur swiftly during stress. This complicates comparison between cortisol responses to ACTH and to critical disease. Based on published studies it is discussed whether the outcome of an ACTH test is an appropriate indicator of the need for glucocorticosteroid replacement. This issue is of particular importance when deciding if permanent glucocorticosteroid substitution is necessary or not.