Endocrine Abstracts

Background: The insulin tolerance test (ITT) is considered the gold standard test for evaluating the ACTH–cortisol axis in patients with pituitary disease. However, the test requires time and personnel resources, and has clear contraindications. Therefore, an ACTH stimulation test is often performed instead.

Objective: The objective was to compare the cortisol response acquired by ACTH stimulation and during ITT in patients with pituitary disease.

Methods: In a total of eight patients with acromegaly, both ITT and an ACTH stimulation test were performed during the same week, but on separate days. A total of 20 comparisons were performed, five being preoperative and 15 postoperative.

Results: Five comparisons were excluded for analyses due to inadequate hypoglycaemia. The remaining 15 comparisons were both preoperative (three, including one after octreotide treatment) and postoperative (three at 3 months, three at 1 year and six at 5 years postoperative). During ITT, peak cortisol level was 637/745 nmol/l (mean/median). Peak cortisol after ACTH stimulation was 948/1040 nmol/l. There was significant correlation between highest plasma cortisol during ITT and ACTH stimulation (Spearman’s ρ=0.79 and Pearson’s r=0.86, both P<0.001). At ITT, four test displayed peak cortisol <550 nmol/l, of them only one ACTH stimulation test resulted in peak cortisol <550 nmol/l. The discrepant results were pre-treatment, 3 months and 5 years postoperative.

Conclusion: There is some discrepancy between cortisol response during ITT compared to ACTH stimulation test, where the latter leads to a higher peak cortisol level and less often a blunted response when using the same cut-off level.