Testing Endocrine Function

Prolactin - check prolactin level.

Growth hormone

• Basal growth hormone level does not determine GH deficiency because 50% of a person's GH levels are undetectable in a 24-hour period. At the same time there are pulses of growth hormone secretion which are almost impossible to distinguish from acromegaly.

• Basal IGF - 1 level - useful for deficiency as well as excess of growth hormone secretion. Some clinicians advocate that stimulation testing may not be required in patients with other anterior pituitary hormone deficiencies and a low IGF-1 level.

• Insulin tolerance test - the gold standard test for the diagnosis of GH deficiency.

• GH-releasing hormone-arginine test is as accurate as ITT and it is less dangerous.

• Oral glucose tolerance test showing an elevated IGF-1 value and an elevated GH value with failure to suppress after oral glucose administration is suggestive of acromegaly.

Hypothalmo-pituitary-adrenal axis

Mineralocorticoid deficiency

• Undetectable serum cortisol is diagnostic of adrenal insufficiency. A cortisol > 580 nmol/L precludes the diagnosis of adrenal insufficiency.

• Short synacthen test can be used to confirm the adrenal insufficiency.

Mineralocorticoid excess

• Aldosterone renin ratio is the best screening test for hyperaldosteronism. The ratio is unaffected by most antihypertensive except spironolactone.

• 24 hr urinary aldosterone collection can be confirmatory for hyperaldosteronism.

• Intravenous saline loading test to assess suppression of aldosteronecan also be used to confirm the diagnosis.