Type of test Blood
Normal findings
Increased response to CRH
Test explanation and related physiology
This test is used to differentiate Cushing disease (caused by an ACTH-producing pituitary adenoma) from Cushing syn drome, which has other adrenal causes. CRH and ACTH hormone secretion is part of a well-developed feedback mechanism dependent on the plasma cortisol levels. As plasma cortisol levels increase, CRH and ACTH secretion is suppressed; as cortisol levels decrease, CRH and ACTH secretion is stimulated. In patients with Cushing disease, ACTH and cortisol levels will increase with CRH administration. However, with less than a 50% increase in ACTH, or less than a 20% increase in cortisol, other adrenal causes of Cushing syndrome are suspected.
Procedure and patient care
Before
* Explain the procedure to the patient Instruct the patient to fast for at least 4 hours
• Monitor blood pressure and pulse throughout the testing period
• Establish intravenous (IV) access
• Draw the pretest blood before administration of CRH
• Blood tube commonly used: Lavender for ACTH, gold for cortisol
During
• Administer CRH 1 mcg/kg by IV.
• Obtain ACTH and cortisol blood levels at 15, 30, 45, and 60 minutes after administration of CRH. After
• Apply pressure or a pressure dressing to the venipuncture site.
Abnormal findings
- Cushing syndrome from adrenal-producing tumor
- Cushing syndrome from an ectopic, ACTH-producing tumor
- Cushing disease
