What is the confirmatory test for acromegaly showing lack of GH suppression after glucose?

What is the confirmatory test for acromegaly showing lack of GH suppression after glucose?

• A. Oral glucose suppression test with increased GH
• B. MRI of the pituitary
• C. CT chest
• D. Serum prolactin

Answer: (A)

The test being described relies on how growth hormone responds to a glucose load. In a healthy person, giving an oral glucose load causes growth hormone to drop to very low levels. In acromegaly, typically from a GH-secreting pituitary adenoma, the hormone secretion is autonomous and does not get suppressed by glucose. So during the test, GH fails to fall into the suppressed range and remains elevated, which confirms the diagnosis. In practice, the patient drinks a 75-gram glucose solution, and GH is measured at fasting and at intervals afterward. If the nadir GH after glucose is below about 1 ng/mL (threshold can vary by assay), the test is negative for acromegaly; if GH does not suppress below that level, acromegaly is supported. IGF-1 is often checked first as a screening step, since it tends to be elevated in most patients with acromegaly, but the glucose suppression test provides confirmatory evidence of GH dysregulation. MRI of the pituitary is useful to localize a tumor after diagnosis is established, CT chest is not relevant to diagnosing acromegaly, and serum prolactin might be checked because pituitary adenomas can secrete multiple hormones, but it does not confirm the GH suppression pattern needed for diagnosis.

The test being described relies on how growth hormone responds to a glucose load. In a healthy person, giving an oral glucose load causes growth hormone to drop to very low levels. In acromegaly, typically from a GH-secreting pituitary adenoma, the hormone secretion is autonomous and does not get suppressed by glucose. So during the test, GH fails to fall into the suppressed range and remains elevated, which confirms the diagnosis.

In practice, the patient drinks a 75-gram glucose solution, and GH is measured at fasting and at intervals afterward. If the nadir GH after glucose is below about 1 ng/mL (threshold can vary by assay), the test is negative for acromegaly; if GH does not suppress below that level, acromegaly is supported. IGF-1 is often checked first as a screening step, since it tends to be elevated in most patients with acromegaly, but the glucose suppression test provides confirmatory evidence of GH dysregulation.

MRI of the pituitary is useful to localize a tumor after diagnosis is established, CT chest is not relevant to diagnosing acromegaly, and serum prolactin might be checked because pituitary adenomas can secrete multiple hormones, but it does not confirm the GH suppression pattern needed for diagnosis.