Endocrine Abstracts

Background: The glucagon stimulation test (GST) involves administering an injection of glucagon and monitoring respondent levels of cortisol, growth hormone and glucose in the blood. The levels recorded are compared to current standard recommendations in order to offer a suggestion into growth hormone or cortisol deficiency. Many children who underwent the GST to investigate growth hormone deficiency (GHD) or prior to transfer to adult endocrine clinic failed to reach the adequate cortisol threshold outlined in the test, despite passing other tests to disprove cortisol deficiency. We conducted a pilot study and a literature review to investigate this.

Method: Our pilot study involved 14 children aged 3-18 years who underwent the GST between January 2016 and November 2020. All of the patients had previously shown adequate cortisol readings in alternative testing (Short Synacthen Test or ACTH stimulation test). Of these 14 patients, 5 achieved adequate cortisol readings to pass the test (≥430 nmol/l) and 9 did not reach the threshold so failed the test. Data was collected and comparisons were made between those who passed the test and those who failed. Specifically, we investigated the impact of blood glucose fluctuation and age on cortisol response. Additionally, a literature review was conducted using Embase and Medline looking at existing evidence.

Results: In our pilot study 9/14 patients failed the test, resulting in a 64% false positive cortisol deficiency rate. Mean peak blood glucose was higher in those who passed the GST compared to those who failed however this difference was not significant (P=0.5448). Extent of glycaemic fluctuation was significantly higher in those who passed the test compared to those who failed (P=0.0022). A strong negative correlation was seen between increasing age and peak cortisol (r=0.74).

Conclusion: Results from our pilot study and literature review suggest the need for the cortisol cut-off in the GST to be lowered and individualised to each patient, taking age into consideration. This study is limited by small sample size, so further research and ROC analysis is required in order to suggest more appropriate threshold values.