A comparison between the 1-mu g adrenocorticotropin (ACTH) test, the shortACTH (250 mu g) test, and the insulin tolerance test in the assessment of hypothalamo-pituitary-adrenal axis immediately after pituitary surgery

The short ACTH stimulation test is an easy, reliable, and extensively used test in the assessment of the hypothalamo-pituitary-adrenal (HPA) axis. How ever, its use immediately after pituitary surgery is a matter of debate. Th e insulin tolerance test (ITT) is the gold standard in the evaluation of th e HPA axis, but it is not always without side effects and may be unpleasant early after pituitary surgery. Our aim was to investigate the value of the 1-mu g ACTH test in the assessment of the HPA axis early after pituitary s urgery. We also aimed to determine the value of the 1-mu g and 250-mu g ACT H tests and the ITT in the estimation of HPA axis status after 3 months pos toperatively. Nineteen patients subjected to pituitary tumor surgery were i ncluded in the study, and the ITT and the 1-mu g and 250-mu g ACTH tests we re performed between the 4th and 11th days of surgery. The tests were repea ted at the first month in 3 patients with subnormal peak cortisol responses (454, 125, and 301 nmol/L) and in 18 patients at the third month postopera tively. ACTH stimulation tests were performed by using 1 mu g and 250 mu g ACTH iv as a bolus injection, and blood samples were drawn at 0, 30, and 60 min for measurement of serum cortisol levels. The ITT was performed by usi ng iv regular insulin, and serum glucose and cortisol levels were measured. The 1-mu g and 250-mu g ACTH stimulation tests and the ITT were performed consecutively. At least 48 h were allowed between each test. A peak serum c ortisol level of 550 nmol/L or greater was considered as a normal response for both the ITT and the ACTH tests. The serum cortisol level was measured by RIA using commercial kits. Serum glucose was determined by glucose oxida se method. There were correlations between the peak cortisol response to th e ITT and the 1-mu g ACTH test (r = 0.39, P < 0.05) in the early postoperat ive period. No correlation was found between the ITT and the 250-mu g ACTH test responses. In the early postoperative period, two patients showed norm al cortisol responses (greater than or equal to 550 nmol/L) to the 1-mu g A CTH test and five patients showed normal cortisol responses to the 250-mu g ACTH test among the six patients with subnormal cortisol responses to the ITT. Three patients with subnormal cortisol responses to ITT and baseline c ortisol values less than 240 nmol/L showed normal HPA axis at the end of th e first month. In the late postoperative period, at the third month, all th e patients showed normal HPA axis. In the early postoperative period of pituitary surgery, the 1-mu g ACTH tes t results are more concordant than the 250-mu g ACTH test in comparison wit h the ITT. Our results also indicate that HPA axis dysfunction shown by ACT H stimulation tests and the ITT in early postoperative period may be normal ized 1-3 months after surgery. For this reason, we think that dynamic tests including the ITT may not be useful early after pituitary surgery.