A 42-year-old man has progressive shoe size increase, coarse facial features, headaches, and bitemporal hemianopia. During a 75 g oral glucose tolerance test, his growth hormone concentration fails to fall below 1 ng/mL and instead rises to 12 ng/mL. What does this result demonstrate?
- A Appropriate growth hormone responsiveness confirming the test was performed correctly but excluding acromegaly
- B Normal suppression of growth hormone by the glucose load
- C Autonomous growth hormone secretion that escapes normal hypothalamic suppression ✓
- D Secondary adrenal insufficiency masking the growth hormone response
Correct answer: C. Autonomous growth hormone secretion that escapes normal hypothalamic suppression
Explanation
In healthy subjects, hyperglycemia suppresses growth hormone to below approximately 1 ng/mL through somatostatin-mediated hypothalamic inhibition. Failure to suppress, especially a paradoxical rise, indicates autonomous secretion from a somatotroph adenoma and confirms acromegaly in this clinical setting. Suppression to undetectable levels would argue against the diagnosis, and adrenal insufficiency is irrelevant to the growth hormone response to glucose.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.