Oral glucose tolerance test for growth-hormone suppression (75 g glucose; growth hormone is suppressed to less than 2 µg/L throughout a 2-h test in normal subjects)
Serum or plasma measurement of insulin-like growth factor I [IGF-I] (random blood specimen; significantly elevated level for age and sex is a preferred integrated measure of excess growth hormone)
Serum prolactin measurement
Thyrotropin-releasing hormone (TRH) or gonadotropin-releasing hormone (GnRH) stimulation test to assess paradoxical growth-hormone response
Thyroid function tests (serum thyrotropin, free thyroxine [FT4] or FT4 index tests) and possibly thyrotropin-releasing hormone (TRH) stimulation test
In men, serum total and free testosterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels
In postmenopausal women, serum FSH and LH levels
In premenopausal women with secondary amenorrhea, serum 17 ß-estradiol or progestational challenge
Assessment of the integrity of the hypothalamic-pituitary-adrenal axis (insulin tolerance, metyrapone or cortrosyn stimulation test)
Magnetic resonance imaging (MRI) or computed tomography (CT) of the pituitary fossa. MRI is more sensitive in resolving small tumours and in identifying extension outside of the sella turcica and is therefore preferred
Chest radiograph (to assess cardiac size)
If a tumour is not visible on imaging of the pituitary, but GHRH levels are elevated, CT scans of the chest and abdomen should be performed to identify an ectopic source of GHRH production
Visual fields by perimetry, to assess effect of tumour on optic chiasm
Standard biochemical studies (calcium, phosphorous, glucose, hemoglobin A1c and lipid levels)
Sleep studies to assess presence and severity of sleep apnea