Metyrapone Stimulation Test

Assay for Cortisol and ACTH:

Chemiluminescence Assay (CLIA) .

Assay for 11 DOC:

LC-MS/MS.

Precautions:

Hypotension , nausea, vomiting, abdominal discomfort or cramping, and musculoskeletal pain in patients with adrenal insufficiency may happen. Metyrapone can also cause dizziness, sedation, and allergic rash.

Interpretation:

Metyrapone blocks the conversion of 11-deoxycortisol to cortisol by CYP11B1 (11-beta-hydroxylase, P-450c11), the last step in the synthesis of cortisol, and induces a rapid fall of cortisol and stimulation of ACTH.

A normal response to the overnight single-dose test consists of [1–3]:

A serum cortisol concentration at 8 AM of less than 5 µg/dL (138 nmol/L) confirms adequate metyrapone blockade.
An 8 AM serum 11-DOC concentration > 7 mcg/dL (> 200 nmol/L).

A lack of achieving a serum 11-DOC concentration > 7 mcg/dL in the presence of a serum cortisol > 5 mcg/dL may be related to a lack of adequate 11 beta hydroxylase blockage. In such patients, the test needs to be repeated after taking higher dosage of metyrapone.

Caveats

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