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ITT for GH Deficiency — RACP Adult Medicine MCQ

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HardEndocrinologyITT for GH DeficiencyRACP Adult Medicine

A 45-year-old woman with suspected growth hormone deficiency (post-pituitary surgery for non-functioning adenoma) undergoes an insulin tolerance test (ITT). Adequate hypoglycaemia is achieved (glucose 1.8 mmol/L). Peak GH is 2.5 μg/L. Peak cortisol is 550 nmol/L. What is the interpretation?

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Correct answer: C — Growth hormone deficiency

ITT (gold standard for assessing GH reserve): adequate hypoglycaemia (glucose <2.2 mmol/L) must be achieved. Peak GH <3 μg/L (severe) or <5 μg/L (partial) confirms GHD. This patient's peak GH of 2.5 μg/L = severe GHD. Peak cortisol >450-500 nmol/L excludes ACTH deficiency (cortisol axis intact). GH replacement therapy should be considered if symptomatic.

Reference: Endocrine Society – 2016 – GH Replacement; ESA 2024