THE POTENTIAL FOR SERIOUS CONSEQUENCES FROM MISINTERPRETING NORMAL RESPONSES TO THE RAPID ADRENOCORTICOTROPIN TEST

Despite unequivocal published evidence that patients with subnormal hy pothalamic-pituitary-adrenal (HPA) function may respond normally to AC TH, such normal results are still considered reliable indications of u nimpaired HPA function. This view was tested in four patients with cli nical features suggesting corticotropin deficiency, in whom cosyntropi n (0.25 mg, iv) raised serum cortisol above 560 nmol/L (20 mu g/dL) at 1 h. All four patients had subnormal responses to metyrapone and exce llent persistent improvement during subsequent glucocorticoid therapy. Serum cortisol concentrations 1 h after cosyntropin treatment in thes e patients closely resembled cortisol concentrations 1 h after uncompl icated cholecystectomy in six other patients. However, the rapid ACTH test in the patients with hypopituitarism failed to indicate whether m ore prolonged stimulation by ACTH or their endogenous stress would sti mulate the normal continuing rise in serum cortisol, which reached 135 8 +/- 170 nmol/L (+/- SE) 5 h alter the incision in the cholecystectom ized patients. As the three hypocorticotropic patients who were recogn izably stressed had unstressed serum cortisol levels despite persisten t adrenocortical reserve (shown by their ACTH responses) and recovered during glucocorticoid therapy, the ACTH test, if interpreted to indic ate normal HPA function, would probably have had disastrous consequenc es. We conclude that a normal response to the rapid ACTH test can be d angerously misleading, particularly in incomplete ACTH deficiency stat es.