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The primary test used to confirm acromegaly is the Oral Glucose Tolerance Test (OGTT). In patients suspected of having acromegaly, the diagnosis is supported if there is a lack of suppression of growth hormone levels after glucose administration. Normally, glucose ingestion suppresses growth hormone secretion; however, in individuals with acromegaly, this suppression does not occur. Therefore, when a patient is given glucose and the growth hormone levels remain elevated, this abnormal response is indicative of acromegaly.

Other tests may support the diagnosis or provide additional information, but they do not serve as the primary confirmatory test. For instance, elevated IGF-1 levels can suggest increased growth hormone activity but are not definitive without the functional assessment provided by the OGTT. Similarly, measuring growth hormone levels alone can be misleading, as levels can fluctuate significantly throughout the day. TSH levels are unrelated to acromegaly and are more relevant for thyroid function assessment.