Endocrine Abstracts

Aim: The insulin tolerance test (ITT) is considered the gold standard test in assessing the integrity of the hypothalamic–pituitary–adrenal (HPA) axis. The aim of this study is to evaluate if the 0900 h cortisol levels can be predictive of the patient’s response to hypoglycaemia, minimizing the use of the ITT as it is labour, intensive and unpleasant for the patient.

Methods: This is a retrospective study of 110 ITTs performed at the Endocrine Unit of St James’s Hospital in Leeds between January 2010 and July 2013. The baseline serum cortisol level was compared against the patient’s peak cortisol response to hypoglycaemia (normal ≥500 nmol/l; suboptimal ≥400 nmol/l but <500 nmol/l; and insufficient <400 nmol/l).

Results: Six patients had basal cortisol <100 nmol/l. All of them (100%) failed to respond to hypoglycaemia. 57 had basal cortisol between 100 and 299 nmol/l. Among them, 22 (38.6%) had a normal ITT, 18 (31.6%) had a suboptimal response and 17 (29.8%) had an inadequate response to hypoglycaemia. The remaining 47 patients had baseline cortisol ≥300 nmol/l, with 32 of them (68.1%) responding normally, 14 (29.8%) having a suboptimal response and one patient (2.1%) failing the ITT. The Pearson’s correlation between basal and peak cortisol was calculated at 0.685.

Conclusions: Measurements of basal serum cortisol can identify patients for whom the ITT may not be necessary. Basal cortisol <100 nmol/l indicated a HPA axis insufficiency, whereas levels ≥300 nmol/l suggested an at least suboptimal response to hypoglycaemia, which would allow the use of steroids in the context of an acute illness only. In both groups the ITT could be avoided, as it would not alter patients’ management. On the contrary, baseline cortisol between 100 and 299 nmol/l cannot be used to predict patient’s response to hypoglycaemia, therefore dynamic tests to assess the HPA axis integrity should be performed.