How is acromegaly diagnosed?

If your doctor suspects acromegaly, you should be referred to an endocrinologist. They may measure the Growth Hormone (GH) level in your blood. However, a single blood test of an elevated GH level is not sufficient to diagnose acromegaly, as GH is secreted by the pituitary in spurts and results can vary widely from minute to minute. Insulin growth factor 1 (IGF1) is also measured.

A suppression test, or oral glucose tolerance test, is a more accepted way to measure GH and to diagnose acromegaly. This involves drinking a glucose solution which in healthy people lowers GH levels, but in those with acromegaly this suppression of GH levels does not occur.

IGF-1 levels can also be used, as high levels are a sign of excess GH activity, which is the hallmark of acromegaly.

After acromegaly has been diagnosed by the above testing, an MRI scan of the pituitary is used to locate and detect the size of the tumour causing excessive GH production. Usually an area of pituitary abnormality is seen on the MRI scan but occasionally the tumour is too small to be seen. Very rarely, a tumour elsewhere in the body may produce growth-hormone-releasing hormone which stimulates the pituitary to produce excessive GH. Such very rare tumours will be identified with additional CT or MRI scans.

Further tests such as field of vision tests may be carried out to assess whether the tumour is causing any pressure on the optic nerves, as these nerves pass very close to the pituitary gland.
Other blood tests may be taken to check if other pituitary hormones are affected such as cortisol, thyroid and sex hormones (adrenal, thyroid and ovary testes).