What additional investigation is most likely to confirm a diagnosis of acromegaly?

The most reliable investigation to confirm a diagnosis of acromegaly is the measurement of serum insulin-like growth factor 1 (IGF-1) levels. In acromegaly, there is an excess of growth hormone (GH), which leads to increased production of IGF-1 by the liver. Elevated levels of IGF-1 are consistent throughout the day and are a key indicator of GH activity, providing a more stable assessment than measuring growth hormone itself.

While fasting growth hormone and the growth hormone suppression test can provide additional information, they are less definitive. Fasting growth hormone levels can be variable, and a single measurement can lead to false conclusions. The growth hormone suppression test, which involves measuring GH levels after glucose administration, can help in assessing the somatostatin response to glucose, but it may not always be performed routinely in diagnosing acromegaly.

In contrast, the serum IGF-1 test is widely used because it can effectively indicate chronic growth hormone excess, making it the most straightforward and reliable test for confirming acromegaly.