Question

A 42-year-old woman presents with enlarged hands, coarsened facial features, and increased shoe size. Her IGF-1 level is elevated. Which of the following is the most specific test to confirm the diagnosis?

• A. Measurement of IGF-1 alone
• B. Lack of GH suppression following oral glucose tolerance test (OGTT)
• C. Lack of IGF-1 suppression after OGTT
• D. Random growth hormone level

Hint:

Acromegaly confirmation = failure of GH suppression after oral glucose.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The clinical features (enlarged hands, coarse face, shoe size change) are classic for Acromegaly, usually caused by a Growth Hormone (GH) secreting pituitary adenoma. The question asks for the gold-standard confirmatory test following a suggestive screening result (elevated IGF-1).
Step 2: Detailed Explanation:

Screening: Insulin-like Growth Factor-1 (IGF-1) is the best screening test because its levels are stable throughout the day, unlike GH which is secreted in pulses. An elevated age-matched IGF-1 strongly suggests acromegaly.

Confirmatory Testing (OGTT): The physiological response to a glucose load is the suppression of GH secretion. In patients with acromegaly, the GH secretion from the pituitary tumor is autonomous and fails to suppress.

Procedure: 75g of oral glucose is administered, and GH levels are measured at intervals. In a normal individual, GH levels should drop to < 1 ng/mL (or even < 0.4 ng/mL with highly sensitive assays).

Interpretation: A failure to suppress GH to below the threshold after a glucose load confirms the diagnosis of acromegaly.

Why not others? IGF-1 does not suppress with glucose (Option C). Random GH levels (Option D) are useless because GH can be high in healthy individuals during a secretory pulse or low due to the short half-life between pulses.

Step 3: Final Answer:
The most specific confirmatory test for acromegaly is the Growth Hormone suppression test during an Oral Glucose Tolerance Test (OGTT).