NEET-PG 2025 — Internal Medicine

Question 31: A 30-year-old man develops an increase in shoe size with coarse facies and large hands. IGF1 is elevated. What is the investigation of choice?

• A. Failure to suppress IGF-1 by OGTT
• B. GH levels
• C. Failure to suppress GH by OGTT (Correct Answer)
• D. IGF-1 levels

Explanation: ***Failure to suppress GH by OGTT*** - This is the **gold standard dynamic test** for confirming acromegaly, as it proves autonomous and unregulated **Growth Hormone (GH)** secretion [1]. - In healthy individuals, glucose load suppresses GH levels (typically to <1 ng/mL), but this suppression fails in patients with GH-secreting tumors [1]. *IGF-1 levels* - While highly sensitive for screening and monitoring, elevated **Insulin-like Growth Factor 1 (IGF-1)** levels alone are not definitive for diagnosis [2]. - IGF-1 levels must be confirmed with a dynamic test because they can be influenced by other factors like malnutrition or chronic liver failure [2]. *Failure to suppress IGF-1 by OGTT* - The definitive OGTT suppression test measures the suppression of **GH**, not IGF-1; IGF-1 reflects integrated GH production [1]. - While IGF-1 levels are used for diagnosis and monitoring, measuring its failure to suppress during OGTT is not the primary definition of diagnostic test failure. *GH levels* - A single random measurement of **Growth Hormone (GH)** is unreliable for diagnosis because GH is secreted in a highly pulsatile manner [1]. - Dynamic testing, such as the **Oral Glucose Tolerance Test (OGTT)**, is mandatory to confirm the pathological non-suppressibility of GH [1].