Endocrine Abstracts

Background: The insulin tolerance test (ITT) is regarded as the gold standard in growth hormone stimulation testing. However, it is known that children and adolescents in puberty often exhibit physiological insulin resistance, and therefore theoretically require more insulin to induce the level of hypoglycaemia required in the ITT. Based on this, in 2021 we changed from using 0.10units/kg to 0.15units/kg insulin.

Aim: To evaluate how a dose of 0.10units/kg (Group 1) vs 0.15units/kg of insulin (Group 2) affects the success rate of the ITT in pubertal children considering growth hormone (GH) and glucose responses, and to use the results to inform future dosing in our ITT protocol.

Objectives: 1. To compare the nadir blood glucose (NBG) levels between patients who received a dose of 0.10units/kg vs 0.15units/kg insulin.2. To evaluate growth hormone responses in the two groups.

Method: A retrospective service evaluation (SE) was conducted of the ITTs done over four years (2019-2023 inclusive) within a tertiary paediatric endocrine unit. 80 patients were selected via stratified probability sampling. Inclusion criteria were pubertal patients who had undergone an ITT at a dose of 0.10units/kg or 0.15units/kg of insulin. Data collected included the insulin dose administered, glucose baseline and nadir and the timing to assess whether the ITT had been successful, as well as peak GH levels. Statistical analysis was conducted using the paired T-test.

Results: There were 40 patients selected in each group. Group1: 9.74-18.88 years; (mean 14.79+/-2.5 years); and Group 2: 10.67-18.99 years (mean 15+/-2.37 years). Results showed that the 0.10units/kg insulin dose produced comparable results to 0.15units/kg insulin for both NBG (mean= 2 mmols vs 1.74 mmols; pValue=0.920) and GH (mean=8.38micrograms/l vs 10.79; pValue=0.454). Relatively few patients required on-demand glucose rescue and there were no adverse events.

Conclusion: Both doses of 0.10units/kg insulin and 0.15units/kg insulin provided appropriate hypoglycaemia for a successful ITT. Given the potential risk of severe hypoglycaemia in ITT it is reassuring that a smaller dose of insulin can be used in pubertal patients to elicit sufficient hypoglycemia to support an interpretable ITT. This SE also supports the overall safety of the ITT.