Use of the dexamethasone-adrenocorticotropin test to assess the requirement for continued glucocorticoid replacement therapy after pituitary surgery.

We assessed the need for continued glucocorticoid replacement therapy in postsurgical pituitary tumor patients using a dexamethasone-ACTH test. The patients received 1 mg dexamethasone, orally, at 2300 h and 250 micrograms synthetic ACTH (Cosyntropin), iv, at 0800 h the next morning. The mean +/- SD integrated cortisol response for a 2-h period of the 31 pituitary tumor patients [1264 +/- 924 micrograms X min/dl (34.87 +/- 25.49 mumol X min/liter)] was significantly less (P less than 0.005) than that of 25 normal subjects [3331 +/- 544 micrograms X min/dl (91.90 +/- 17.04 mumol X min/liter)]. Replacement glucocorticoids were abruptly discontinued in 11 patients with responses above 1450 micrograms X min/dl (40.01 mumol X min/liter). No clinical or laboratory evidence of adrenal insufficiency occurred as long as 15 months after discontinuation. Metyrapone tests, however, in the 11 glucocorticoid-withdrawn patients revealed a reduced mean +/- SD serum 11-deoxycortisol level compared with that of 10 normal subjects [8.9 +/- 4.7 vs. 15.6 +/- 5.0 micrograms/dl (0.26 +/- 0.13 vs. 0.45 +/- 0.16 mumol/liter); P less than 0.005]. Our results indicate that the dexamethasone-ACTH test is useful in identifying patients in whom replacement glucocorticoid therapy can be safely withdrawn under nonstressed conditions. The test can be simplified to one plasma cortisol level determined 30 min after ACTH administration.