Metyrapone test

This is a test for Cushing's syndrome that is now rarely used.

Metyrapone inhibits 11-beta-hydroxylation in the adrenal cortex and hence cortisol and corticosterone synthesis. A low corticosteroid level causes increased ACTH secretion and therefore adrenal stimulation and further 11-deoxycortisol production (since cortisol production is blocked). The metabolites of 11-deoxycortisol (17-hydroxy and 17-ketogenic steroids) are excreted in the urine.

Interpretation of test results:

• normal individuals - increased levels of metabolites
• adrenal hyperplasia - Cushing's disease - higher levels of metabolites
• if Cushing's syndrome is due to ectopic ACTH production, an adrenal adenoma, or adrenal carcinoma, then there is characteristically little or no increased levels of metabolites after metyrapone
• reduced responses to metyrapone may be seen in:
  • hypopituitarism
  • primary thyrotoxicosis
  • pregnancy (but metyrapone is contraindicated in these patients)
  • some patients taking phenytoin or the oral contraceptive pill