Normal Values:

Cortisol levels should decrease after you receive dexamethasone.

Low dose:

• Overnight: 8 a.m. plasma cortisol < 1.8 mcg/dl
• Standard: Urinary free cortisol on day 3 < 10 mcg/day

High dose:

• Overnight: > 50% reduction in plasma cortisol
• Standard: > 90% reduction in urinary free cortisol

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What abnormal results mean:

An abnormal response to the low-dose test may mean that you have abnormal release of cortisol (Cushing syndrome). This could be due to:

• Adrenal tumor that produces cortisol
• Pituitary tumor that produces ACTH
• Tumor in the body that produces ACTH

The high-dose test can help tell a pituitary cause (Cushing's disease) from other causes.

Abnormal results vary based on the condition causing the problem.

Cushing syndrome caused by an adrenal tumor:

• Low-dose test: no change
• High-dose test: no change

Cushing syndrome related to an ectopic ACTH-producing tumor:

• Low-dose test: no change
• High-dose test: no change

Cushing syndrome caused by a pituitary tumor (Cushing's disease)

• Low-dose test: no change
• High-dose test: normal suppression