Adrenocorticotropic hormone stimulation test during high-dose glucocorticoid therapy.

Objective: To define the effective time frame of adequate serum cortisol response to the short standard 250-microg adrenocorticotropic hormone stimulation test (ACTH-ST) after initiation of high-dose glucocorticoid therapy in order to assist in the diagnosis of adrenal insufficiency.

Methods: We performed an ACTH-ST at 4 different times in hospitalized patients, who had a documented intact hypothalamic-pituitary-adrenal axis and were receiving high-dose dexamethasone therapy for nonendocrine diseases, to determine the time until the serum cortisol response is compromised. The ACTH-ST was performed at the following time intervals after initiation of dexamethasone therapy - 24, 48, 72, and 96 hours. The outcome measures were cortisol levels measured at 0, 30, and 60 minutes after administration of 250 microg of cosyntropin.

Results: Of the overall group of 11 study patients, all those (n = 8) tested within the first 72 hours after initiation of dexamethasone therapy had an adequate response (serum cortisol level at 60 minutes, >or=18 microg/dL). Two of the 3 patients tested at 96 hours after initiation of dexamethasone therapy had a suppressed cortisol response at 60 minutes. At 30 minutes, all cortisol levels except 1 were inadequate (<18 micro/dL).

Conclusion: This study suggests indirectly that the ACTH-ST may be used for the diagnosis of suspected adrenal insufficiency within the first 3 days after initiation of empiric glucocorticoid therapy. An inadequate response of serum cortisol at 60 minutes to the ACTH-ST may be indicative of adrenal insufficiency in this setting. Additional studies with more patients in each therapy time point are needed to confirm these initial results.