Evaluation of the hypothalamo-pituitary-adrenal axis: the insulin tolerance test and beyond.

Assessment of the hypothalamo-pituitary-adrenal axis is essential to determine the strength of the adrenocorticotrophic hormone (ACTH) reserve in relation to clinical and subclinical hypocortisolaemia. The insulin tolerance test has been established as the gold standard; however, the time and the potential hazards involved have led to a search for more viable alternatives. Numerous tests have evolved, which include the 8 a.m. fasting plasma cortisol, standard short synacthen test, low dose (1 microgram) synacthen test, metyrapone provocation and glucagon stimulation test. The low-dose (1 microgram) synacthen stimulation test has emerged as a potential alternative but further well designed trials are required to establish this.