An acromegaly test primarily involves measuring growth hormone (GH) levels, especially through a growth hormone suppression test, to confirm a diagnosis. An elevated Insulin-like Growth Factor 1 (IGF-1) level initially suggests the condition.
Understanding the Acromegaly Test
Acromegaly is a hormonal disorder that develops when your pituitary gland produces too much growth hormone during adulthood. Because excessive GH leads to increased IGF-1 production, both GH and IGF-1 levels are important in diagnosing acromegaly.
Initial Screening: IGF-1 Measurement
- Purpose: To initially screen for acromegaly.
- Procedure: A blood test measures the level of IGF-1 in the blood.
- Interpretation: An elevated IGF-1 level, compared to age and sex-matched normal values, suggests the possibility of acromegaly. This warrants further testing.
Confirmatory Test: Growth Hormone Suppression Test (Oral Glucose Tolerance Test - OGTT)
- Purpose: To confirm the diagnosis of acromegaly. This is the most reliable test.
- Procedure:
- A baseline GH blood level is measured.
- The patient drinks a preparation of glucose (sugar).
- GH blood levels are then measured at specific intervals (e.g., every 30 minutes for 2 hours) after glucose ingestion.
- Interpretation:
- In healthy individuals, the glucose load should suppress GH production to below 1 ng/mL (or sometimes <0.4 ng/mL depending on the lab).
- In patients with acromegaly, GH levels will not suppress adequately and may remain elevated or even increase. Failure to suppress GH below 1 ng/mL strongly suggests acromegaly.
Other Tests
While IGF-1 and the GH suppression test are the mainstays of acromegaly diagnosis, other tests may be performed to investigate the cause or complications of the condition:
- MRI of the Pituitary Gland: To visualize the pituitary gland and identify any tumors (adenomas) that may be causing the excess GH production.
- Other Hormone Level Tests: To assess the function of the pituitary gland and rule out other hormonal disorders.
- Visual Field Testing: To check for any compression of the optic nerves by a pituitary tumor, which can affect vision.
In summary, the acromegaly test typically involves an initial IGF-1 blood test followed by a confirmatory growth hormone suppression test if the IGF-1 is elevated. Other tests might be needed to identify the cause and any complications.
