Insulin tolerance test interpretation — SCE Endocrinology MCQ

Correct answer: A — Impaired ACTH and growth-hormone reserve after adequate hypoglycaemia

The best answer is “Impaired ACTH and growth-hormone reserve after adequate hypoglycaemia”. Symptomatic biochemical hypoglycaemia provides an adequate stimulus, while both peak cortisol and growth hormone are below commonly accepted assay-dependent responses; the clinical setting therefore supports combined anterior-pituitary reserve failure. “The test is uninterpretable because glucose did not fall below 1.0 mmol/L” is less appropriate because a glucose nadir below about 2.2 mmol/L with symptoms is generally an adequate stimulus and deeper hypoglycaemia adds risk “The result establishes primary adrenal failure with preserved pituitary function” is less appropriate because the combined low growth-hormone response and pituitary history point away from isolated primary adrenal disease “Both cortisol and growth-hormone responses are normal for adequate hypoglycaemia” is less appropriate because both stimulated peaks are clearly subnormal and require assay-appropriate endocrine interpretation “The result diagnoses isolated thyrotropin deficiency” is less appropriate because an insulin tolerance test assesses cortisol and growth-hormone reserve, not TSH secretion

Reference: Endotext: Endocrine testing protocols — hypothalamic pituitary adrenal axis. https://www.ncbi.nlm.nih.gov/books/NBK278940/