A random high growth hormone is of no diagnostic value due to the large physiological variations in normal growth hormone levels. An important test in the diagnosis of acromegaly is the glucose tolerance test. The patient is given a 75g glucose meal, and blood tests are taken at half-hourly intervals. In a normal patient the growth hormone levels will be suppressed, but in the acromegaly patient the growth hormone levels are unsuppressable.
Another unique test that can be used in the diagnosis of acromegaly is by the administration of TRH. This is a unique test as only in acromegaly will there be a doubling of the blood levels of growth hormone.
Another test that is routinely done is the blood level of the somatomedins (IGF-1) which will almost always be raised in acromegaly.
Imaging is obviously a very important part of the diagnosis. A routine plain radiograph of the skull will show an enlarged pituitary fossa in approximately 70% of patients with acromegaly. The best way to identify the tumour is by using a CT scan or an MRI scan.