A 35-year-old man with acromegaly undergoes an oral glucose tolerance test (75 g glucose). Which GH pattern is DIAGNOSTIC of acromegaly?
- A GH fails to suppress below 1 ng/mL (or paradoxically rises) after glucose load ✓
- B GH suppresses to < 1 ng/mL at 60–120 minutes after glucose load
- C GH peaks at 30 minutes then falls to baseline at 120 minutes
- D GH is uniformly suppressed to undetectable levels throughout the test
Correct answer: A. GH fails to suppress below 1 ng/mL (or paradoxically rises) after glucose load
Explanation
In normal individuals, hyperglycemia during OGTT suppresses GH to < 1 ng/mL (some guidelines < 0.4 ng/mL with ultrasensitive assays). In acromegaly, the autonomous GH-secreting tumor fails to suppress — GH remains elevated or even paradoxically rises. This paradoxical GH rise to glucose (seen in ~25% of acromegalics) reflects abnormal somatotroph signaling. OGTT-based GH suppression is the confirmatory test for acromegaly.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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