Diagnosing Cushing syndrome can be complex and difficult. This syndrome is more easily recognized when it is fully developed, but health care providers try to diagnose and treat it well before then. No single laboratory test is perfect in diagnosing the condition, so the health care provider may try different tests.
You will give your health care provider a complete list of all medications and other treatments you have taken to see if any of them could be responsible for raising your cortisol levels. Make certain your list includes everything containing cortisol-like compounds, such as joint or nerve injections received for pain, “tonics” and herbal medications, high doses of progesterone, and skin creams (including bleaching agents).1
You will undergo a test that measures cortisol levels, and a laboratory will check to see if the cortisol levels are normal. This test might be one of the following:
Urine Cortisol Test
Urine samples are collected and tested several times over 24 hours.
Late-night Salivary Cortisol Test
A special device is used for collecting saliva late at night. The sample can be mailed to a laboratory or delivered to the health care provider.
A Test Using Dexamethasone (pronounced dek-suh-METH-uh-sohn)
This test might be called a 1 mg overnight suppression test or a 2 mg 48-hour suppression test. Several hours after you take the synthetic glucocorticoid dexamethasone by mouth, your blood level of cortisol is measured.
If your results are not normal, your health care provider may do further tests or refer you to a specialist—an endocrinologist (pronounced en-doh-kruh-NOL-uh-jist)—for the tests, which might include:
- Another test from Step 2
- Serum midnight cortisol test, which measures blood levels of cortisol late at night
- Dexamethasone-corticotropin-releasing hormone (Dex-CRH) test, which distinguishes between cells produced by tumors and normal cells
If your cortisol levels are persistently above normal and you receive a diagnosis of Cushing syndrome, your health care specialist will check for the cause. Tests might include the following:
- CRH stimulation test
- High-dose dexamethasone suppression test
- Radiologic imaging to see the glands that might be causing symptoms
- Petrosal (pronounced pi-TROH-suhl) sinus sampling to visualize the pituitary gland
- Blood sampling to confirm the pituitary gland is making too much ACTH
Different Testing Steps
If you have certain medical conditions, your health care provider may not use some of the tests listed above for reasons of safety or effectiveness. These conditions can include:
- Renal failure
- Cyclic Cushing syndrome, in which cortisol is sometimes normal and sometimes high
- Adrenal incidentaloma (pronounced in-si-DEN-tl-OH-muh)
Several kinds of medications unrelated to Cushing syndrome may interfere with test results, but your health care provider should be aware of these drugs and know whether you are taking them.1
- Nieman, L. K., Biller, B. M. K., Findling, J. W., Newell-Price, J., Savage, M. O., et al. (2008). The diagnosis of Cushing’s syndrome: An Endocrine Society clinical practice guideline. Retrieved April 8, 2012, from http://press.endocrine.org/doi/abs/10.1210/jc.2008-0125 .
- Boscaro, M., & Arnaldi, G. (2009). Approach to the patient with possible Cushing’s syndrome. Journal of Clinical Endocrinology and Metabolism, 94(9), 3121-3131. PMID 19734443.
- Mayo Clinic. (n.d.). Case detection of Cushing syndrome in adults. Retrieved April 8, 2012, from http://www.mayoclinic.org/medicalprofs/cushing-syndrome.html.