PANCE Endocrinology Practice Test

After an elevated IGF-1 level suggests acromegaly, what is the next step to confirm?

MRI pituitary with contrast first Bone density scan Serum prolactin elevation Lack of suppression of GH on an oral glucose tolerance test

Correct Answer:

Lack of suppression of GH on an oral glucose tolerance test

Explanation:

Elevated IGF-1 indicates GH excess but doesn’t prove active acromegaly on its own. The next step is a dynamic test that shows whether GH secretion is truly autonomous: an oral glucose tolerance test with measurement of GH. In normal individuals, glucose intake suppresses GH to very low levels. In acromegaly, GH fails to suppress (typically remaining elevated, not dropping below about 1 ng/mL). This lack of suppression confirms biochemical acromegaly. After this confirmation, pituitary MRI with contrast is used to locate the adenoma. The other options don’t provide the confirmatory evidence needed: bone density assesses complications, prolactin elevation isn’t diagnostic of GH excess, and MRI is done after confirming the diagnosis.

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