A 46-year-old man has enlarged hands and feet, frontal bossing, and bitemporal visual field loss. Random growth hormone is 12 ng/mL and IGF-1 is markedly elevated for age. Which single result definitively confirms acromegaly?
- A Paradoxical growth hormone rise after thyrotropin-releasing hormone injection
- B Random growth hormone above 10 ng/mL on repeat sampling
- C Failure of growth hormone to suppress below 1 ng/mL after a 75 g oral glucose load ✓
- D Elevated IGF-1 on two separate occasions
Correct answer: C. Failure of growth hormone to suppress below 1 ng/mL after a 75 g oral glucose load
Explanation
The oral glucose tolerance test remains the confirmatory dynamic test: normal subjects suppress GH below 1 ng/mL with modern assays, while acromegalics fail to suppress or show paradoxical elevation. Random GH is useless because secretion is pulsatile and a single value cannot diagnose or exclude the disease, eliminating option B. Elevated IGF-1 supports the diagnosis and correlates with disease activity but is not the definitive standalone confirmation. TRH stimulation testing is obsolete for routine diagnosis.
Reference: Williams Textbook of Endocrinology, 14th ed.
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