After an elevated IGF-1 level suggests acromegaly, which test is used to confirm GH excess?

• A. Oral glucose tolerance test showing failure to suppress GH.
• B. Serum IGF-1 level.
• C. Pituitary MRI.
• D. Random GH measurement.

Answer: (A)

The test to confirm GH excess is an oral glucose tolerance test showing failure to suppress GH. IGF-1 reflects long-term GH action and is useful for screening, but it isn’t definitive because it can be influenced by age, nutrition, and other factors. GH, however, is secreted in pulses, so a single random measurement isn’t reliable for confirming excess.

In an oral glucose tolerance test, a standard glucose load (about 75 g) is given, and GH is measured at baseline and after glucose. In healthy individuals, glucose suppresses GH so the nadir falls well below the normal threshold. In someone with GH-secreting activity (like a pituitary adenoma causing acromegaly), GH does not adequately suppress. This failure to suppress confirms GH excess. The exact cutoff can vary by assay, but the principle remains: lack of GH suppression after glucose proves GH excess.

The other options don’t fit as confirmation because IGF-1 elevation is nonspecific, MRI shows anatomy but not hormone activity, and a random GH level can be misleading due to pulsatile secretion.