Patient Preparation: CRH at a dose of 1 µg/kg of body weight is injected intravenously. This is usually done in the morning at 0900 or the evening at 2000.
Specimen Collection: Plasma with heparin anticoagulation is collected as follows:
(1) baseline: 15 minutes and 1 minute before injection
(2) response curve: 5, 15, 30, 60 and 120 minutes after injection
Testing Performed: Measurements of ACTH and cortisol are performed on each sample.
Interpretation:
• Normal persons show peak levels of ACTH and cortisol 2-4 times baseline levels, with the peak in ACTH occurring at 15-30 minutes after injection and the cortisol peak occurring 60 minutes after injection.
• Patients with ectopic ACTH secreting tumors or adrenal tumors do not show a response to the CRH.
• Patients with pituitary ACTH secreting adenomas show a normal or exaggerated response.
• Patients with pituitary ACTH deficiency show decreased response in both ACTH and cortisol.
• Patients with hypothalamic disease can show a prolonged release of ACTH but a reduced cortisol response.
• Testing may be done in conjunction with dexamethasone suppression testing to distinguish between pituitary Cushing's disease and an ectopic ACTH secreting tumor.
