Background & objectives: One microgram short synacthene test is widely recommended as a screening test for evaluation of hypothalamo-pituitary-adrenocortical axis in patients with secondary adrenal insufficiency. Information on adequacy of cortisol response to this dose at different periods of the day in patients with hypothalamic-pituitary disorders is not available. Hence, this study was designed to assess the adequacy of cortisol response to 1 microg 1-24 adrenocorticotropin (ACTH) at 0800 h and 1600 h in patients with sellar and suprasellar mass lesions.
Methods: Thirty five consecutive patients with sellar and suprasellar mass lesions with mean age of 43.0+/-14.4 yr and 36 healthy controls with mean age of 32.3+/-9.0 yr were studied after obtaining informed consent. Maintenance doses of glucocorticoids in these patients were discontinued appropriately. On day 1, prestimulated and stimulated plasma cortisol samples at 0800 h and at 30 and 60 min following i.v. bolus of 1 microg 1-24 ACTH were collected. While on day 3, plasma cortisol samples were similarly collected at 1600 h. Cortisol estimation was done by a sensitive and specific radioimmunoassay. Stimulated plasma cortisol of 500 nmol/l or higher was defined as a normal response.
Results: In healthy controls, the prestimulated and peak cortisol levels at 0800 h (377.5+/-93.3 and 729.1+/-183.2 nmol/l) were higher (P<0.001 and P<0.01) than those at 1600 h (230.1+/-75.7 and 665.8+/-138.6 nmol/l). All subjects had a cortisol response of 500 nmol/l or higher in response to 1 microg 1-24 ACTH both at 0800 and 1600 h. In the patients' group, the prestimulated plasma cortisol at 0800 h (250.3+/-169.7 nmol/l) was higher (P<0.001) than that at 1600 h (166.3+/-128.9 nmol/l), while the peak cortisol response was comparable (P>0.05) in the morning as well as in the evening (490.9+/-309.4 vs 464.8+/-318.4). In 27 patients (77%) the morning and evening stimulated cortisol response to 1 microg 1-24 ACTH was consistent (normal in 13 and subnormal in 14) but was discrepant in the remaining 8 (23%). In 7 of these 8 patients, cortisol response was normal at 0800 h but not at 1600 h, while in only one, normal response was seen at 1600 h but not at 0800 h.
Interpretation & conclusion: The demonstration of normal peak cortisol response to 1 microg 1-24 ACTH at 0800 h but not at 1600 h in substantial number of patients with sellar and suprasellar mass lesions suggests preference to morning for performing this test.