What is a typical next step to confirm acromegaly after an elevated IGF-1?

• A. Oral glucose tolerance test with failure to suppress GH
• B. CT scan of chest
• C. Serum cortisol
• D. 24-hour urinary calcium

Answer: (A)

Elevated IGF-1 indicates growth hormone (GH) excess, but confirming active acromegaly requires demonstrating that GH production is not properly suppressed. An oral glucose tolerance test is used here: after giving a standard 75 g glucose load, GH and glucose are measured over about two hours. In people without acromegaly, GH falls to very low levels (near undetectable) as glucose rises. In acromegaly, GH remains elevated and fails to suppress. This failure to suppress GH after glucose confirms biochemical activity of GH excess and supports the diagnosis.

After this confirmation, imaging of the pituitary, typically with MRI, is pursued to identify an adenoma. The other tests listed (CT chest, serum cortisol, 24-hour urinary calcium) assess other endocrine issues and do not establish or confirm acromegaly.