Dexamethasone Suppressed CRH Stimulation Test

Indication: Differential diagnosis of pseudo-Cushing's syndrome from Cushing syndrome. To identify the recurrence of Cushing's syndrome.

Procedure:

1. Day 1 - Dexamethasone 0.5mg 6 a.m., 12 noon, 6 p.m. and 12 midnight
2. Day 2 - Begin 24-hr urine collection at 6a.m., wasting first void. Continue taking Dexamethasone 0.5mg 6 a.m., 12 noon, 6 p.m. and 12 midnight
3. Day 3 - stop 24-hr urine collection at 6 am. Last dose of Dexamethasone 0.5mg 6 a.m. 0800
4. Insert saline lock into peripheral vein
5. Inject 1ug/kg of CRH through saline lock, 100mcg - maximum dose
6. Inject 3cc 0.9% NaCL through saline lock to prevent blood from clotting
7. Waste 5cc of blood
8. At 15 minutes draw Cortisol level (red top tube)
9. Discontinue saline lock

Interpretation: A Cortisol level greater than 1.4 mcg/dl suggests the presence of Cushing's syndrome. A Cortisol level less than 1.4mcg/dl suggests pseudo-Cushing's syndrome or non-recurrence of Cushing's syndrome.