Confirmatory investigation for acromegaly is-
**Core Concept**
Acromegaly is a disorder caused by excess growth hormone (GH) production, typically due to a pituitary adenoma. Confirmatory investigations aim to establish the presence of GH excess and its effects on the body.
**Why the Correct Answer is Right**
The gold standard for confirming acromegaly is a 24-hour integrated GH level, measured by a sensitive assay. Normal GH levels typically decline after a glucose load. In acromegaly, GH levels remain elevated due to its autonomous production. This is because glucose suppresses normal GH secretion through a negative feedback mechanism involving the hypothalamic-pituitary axis, particularly somatostatin. The 24-hour integrated GH level helps differentiate between physiological and pathological GH secretion.
**Why Each Wrong Option is Incorrect**
**Option A:** Insulin-like growth factor 1 (IGF-1) levels are often elevated in acromegaly, but they can also be normal or mildly elevated in other conditions. Therefore, IGF-1 alone is not a confirmatory test for acromegaly.
**Option B:** A random GH level is not reliable for diagnosing acromegaly due to its pulsatile nature and diurnal variation. It can be elevated in normal individuals, especially after exercise or stress.
**Option C:** A glucose tolerance test (GTT) can help differentiate between GH hypersecretion and pseudohyperscretion, but it is not a confirmatory test for acromegaly.
**Clinical Pearl / High-Yield Fact**
Remember that a 24-hour integrated GH level is the most reliable confirmatory test for acromegaly, especially when combined with clinical features and imaging studies.
**Correct Answer:** C. Glucose tolerance test (GTT) can help differentiate between GH hypersecretion and pseudohyperscretion, but it is not a confirmatory test for acromegaly.