Cortisol levels in central adrenal insufficiency: light and shade

Evaluating children or adolescents with central adrenal insufficiency (CAI) is a difficult task in clinical practice, especially in subjects with hypothalamic-pituitary diseases and partial ACTH deficiency, or in those with recent pituitary surgery or brain irradiation when the adrenal cortex may still be responsive to stress. In 2008, a meta-analysis reported a three-step approach for evaluating patients at risk for CAI with no acute illness. In particular, the authors recommended the evaluation of morning cortisol, a low dose ACTH test (LDST) and the "gold standard" insulin tolerance test or metyrapone test if the low LDCT was not diagnostic. Cortisol and ACTH secretion exhibit significant fluctuation throughout the day. The reference ranges supplied by labs are so wide that they only flag up extremely low cortisol levels. Interpreting the results correctly can be difficult for a physician without an experience in adrenal dysfunctions. The lack of uniformity in these cut-off levels could in part be attributed to differences in study populations, variability of dynainic tests, the use of different serum cortisol assays and dissimilar cut-off peak serum cortisol response indicative of a normal axis response and the difference in the clinical context in which the studies were done. Therefore, Laboratories have to advertise the need to establish reference values for given populations, both for basal or stimulated hormone levels. Failure to apply this rule may elicit false-positive and more critically, false-negative results. LDST (1 pg synthetic ACTH as iv bolus with measurement of serum cortisol) has been proposed as a sensitive test for the diagnosis of CAl. However, the advantage of LDST compared with the high dose test may be offset by the technical difficulties inherent to dilution of 250 pg ampoules. Clinical judgment remains imperative especially regarding the use of glucocorticoid supplementation during extreme stress.