Metyrapone can be used in the diagnosis of adrenal insufficiency. Metyrapone 30 mg/kg, maximum dose 3,000 mg, is administered at midnight usually with a snack. The plasma cortisol and 11-deoxycortisol are measured the next morning between 8:00 and 9:00 am. A plasma cortisol less than 220 nmol/l indicates adequate inhibition of 11β-hydroxylase. In patients with intact Hypothalamo-pituitary-adrenal axis, CRH and ACTH levels rise as a response to the falling cortisol levels. This results in an increase of the steroid precursors in the pathway. Therefore, if 11-deoxycortisol levels do not rise and remain less than 7 µg/dl (202 nmol/l) and adrenocorticotropic hormone (ACTH) rises, then it is highly suggestive of adrenal insufficiency. If neither 11-deoxycortisol nor ACTH rise, it is highly suggestive of an impaired hypothalamic–pituitary–adrenal axis at either the pituitary or hypothalamus.