metyrapone stimulation test

Indications: - diagnosis of pituitary Cushing's disease Contraindications: - DO NOT PERFORM TEST IF PRIMARY ADRENAL INSUFFICIENCY IS LIKELY - normal response to exogenous ACTH should be demonstrated BEFORE performing test Reference interval: 1) standard multiple dose testing a) serum: 1] 11-deoxycortisol: > 7 ug/dL (202 nmol/L) 2] cortisol: < 3 ug/dL (< 83 nmol/L) c) 24 hour urine 1] 17-hydroxycorticosteroids: 2-4X base level 2] 17-ketosteroids: > 2X base level 3] 17-ketogenic steroids: 2.5-3 fold rise (> 10 mg/day) 2) single dose testing -> serum: 1] 11-deoxycortisol: > 7 ug/dL (202 nmol/L) 2] cortisol: < 3 ug/dL (< 83 nmol/L) 3] ACTH > 150 pg/mL (> 33 pmol/L) Clinical significance: 1) no or impaired response: a) chemical interferences -> amitriptyline, chlordiazepoxide, estrogens, glucocorticoids, methysergide, oral contraceptives, phenobarbital, phenothiazines, phenytoin, progestins, rifampin b) clinical disorders - hypopituitarism - Cushing's syndrome caused by adrenal tumors or ectopic ACTH-secreting tumors 2) Exaggerated response -> clinical disorders -> pituitary Cushing's syndrome Procedure: 1) standard multiple dose testing a) collect baseline urine specimen b) metyrapone 750 mg PO q4h x 6 (children 15 mg/kg) c) collect serum for 11-deoxycortisol, cortisol at 0800 hours the following morning d) collect 24 hour urine (multiple dose) for: 1] 17-hydroxycorticosteroids 2] 17-ketosteroids 3] 17-ketogenic steroids 2) single dose testing a) 30 mg/kg PO with milk or snack at midnight b) collect plasma for 11-deoxycortisol, cortisol & ACTH at 0800 hours the following morning * To ensure accuracy of 24 hours urine collections & to monitor for adverse effects, the standard test should be done on hospitalized patients. The single-dose test may be done on outpatients.

General

special chemistry test

References

Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed., W.B. Saunders, 1995

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