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OGTT for Acromegaly — RACP Adult Medicine MCQ

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ModerateEndocrinologyOGTT for AcromegalyRACP Adult Medicine

A 40-year-old man with suspected acromegaly has an elevated IGF-1 level. An oral glucose tolerance test (OGTT) is performed: baseline GH 8.5 μg/L, nadir GH after 75 g glucose load at 2 hours is 3.2 μg/L. What is the interpretation?

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Correct answer: B — Failure of GH suppression — acromegaly confirmed

Failure of GH to suppress to <1.0 μg/L (some guidelines <0.4 μg/L with ultrasensitive assays) during OGTT confirms autonomous GH secretion consistent with acromegaly. Normal individuals suppress GH to <1.0 μg/L after glucose loading. This patient's nadir of 3.2 μg/L confirms the diagnosis. Pituitary MRI is the next step to identify the GH-secreting adenoma. Treatment is transsphenoidal surgery.

Reference: Endocrine Society – 2014 – Acromegaly Guidelines; ESA 2024