Adrenocortical insufficiency after pituitary surgery: an audit of the reliability of the conventional short synacthen test

Background Assessment of the hypothalamic-pituitary-adrenal (HPA) axis after pituitary surgery is important for appropriate decision making regarding replacement therapy. The synacthen test is often used but is questioned, as time has to elapse for adrenal atrophy to develop. Objective To audit the use of the 250 mu g synacthen test after transsphenoidal adenomectomy. Methods A retrospective study of 110 patients submitted to first-time transsphenoidal adenomectomy. Anterior pituitary testing was performed preoperatively, 1 week and 1, 3, 6 and 12 months postoperatively. The adrenocortical function was tested by a synacthen test (250 mu g synacthen i.v.). Results Thirty-two out of 71 patients with normal HPA function before surgery developed insufficiency postoperatively, seven patients presenting an insufficient test response after 1 week, 16 after 1 month and nine after 3 months, whereas none became insufficient during the remaining follow-up. Three patients presented symptomatic adrenal insufficiency during the first postoperative week despite a normal test. All of these developed an insufficient test 1 month postoperatively. A 1-week basal plasma cortisol > 400 nmol/l indicated HPA sufficiency, whereas a basal cortisol <= 100 nmol/l indicated insufficiency when related to the diagnosis based on the 3-month synacthen test. Conclusion This study confirms that the synacthen test is of limited use in the early postoperative phase, because out of 62 patients with normal 1-week postoperative synacthen responses, 23 patients developed a test that was indicative of adrenal insufficiency over 1-3 months. Our results indicate that a large proportion of patients should be considered for hydrocortisone replacement therapy up to 3 months postoperatively followed by reassessment of the HPA axis.