Tests for Cushing's Syndrome
Cushing's syndrome may not be easy to diagnose.1-3 In fact, some people who have Cushing's syndrome go years before getting diagnosed.1 During the process of being diagnosed, patients can expect many lab tests and multiple visits to various healthcare professionals.3,4
Your healthcare professional may refer you to an endocrinologist, a specialist in the field of hormone function and disease.2,4
If initial tests show high cortisol levels, an endocrinologist may need to do more specialized lab work in order to determine the cause of the increase.2
Why so many tests? The main reason is that symptoms associated with Cushing's syndrome are commonly found among the general population and are associated with many other conditions.1,3
Your healthcare professional may order multiple lab tests to rule out these other conditions.2 Another reason for more than one test is that cortisol levels can vary depending on the time of day they are measured.3
In healthy people, cortisol levels begin to rise in predawn hours, reach their peak in the early morning, and then decrease to reach their lowest levels around midnight.5
For these reasons, your healthcare professional may ask you to take more than one test in order to collect the best data possible.
Tests for identifying the presence of Cushing's syndrome
The tests below are commonly used to see if you may have Cushing's syndrome. When undergoing any testing, it's important to follow the instructions precisely in order to ensure the most reliable results.
Late-Night Salivary Cortisol
This test involves a special home kit used to collect saliva during the late evening when cortisol levels in a healthy person tend to drop.6,7 Keep in mind that your healthcare professional may ask you to take this test more than once in order to ensure accuracy.
24-Hour Urine Free Cortisol
This test involves collecting all of your urine for a 24-hour period in order to measure cortisol. This allows your healthcare professional to see if your body is producing excessive amounts of cortisol. Your healthcare professional may ask you to take this test more than once in order to ensure accuracy.6
Low-Dose Dexamethasone Suppression Testing
Dexamethasone is a drug that mimics cortisol. In this test, a small tablet of dexamethasone will be administered and cortisol levels will be monitored. In a healthy person, cortisol levels normally drop after they receive a low dose of dexamethasone. But for most people with Cushing's syndrome, these cortisol levels will not decrease.3
Dexamethasone CRH Test
This test is performed to help separate cases that look like Cushing's syndrome from actual Cushing's syndrome. The test includes both the low-dose dexamethasone suppression test and a test that stimulates corticotropin-releasing hormone (CRH). Dexamethasone is given first to bring down levels of cortisone, and then CRH is injected. Patients with Cushing's syndrome will usually show high levels of cortisol, while levels in those who do not have Cushing's syndrome will stay low.1,6,7
When undergoing any testing, it's important to follow the instructions precisely in order to ensure the most reliable results.
- Nieman LK, Biller BMK, Findling JW, et al, eds. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline. Chevy Chase, MD: The Endocrine Society; 2008. https://www.endocrine.org/~/media/endosociety/Files/Publications/Clinical%20Practice%20Guidelines/Cushings_Guideline.pdf. Accessed April 13, 2013.
- Adrenal diseases: Cushing's syndrome. The facts you need to know. National Adrenal Diseases Foundation Web site. http://www.nadf.us/diseases/cushings.htm. Accessed April 13, 2013.
- Cushing's Syndrome and Cushing's Disease: Your Question's Answered. The Pituitary Society Web site. http://www.pituitarysociety.org/public/specific/cushing/cushings.pdf. Accessed April 13, 2013.
- Frequently asked questions about transsphenoidal surgery for pituitary adenomas. Massachusetts General Hospital Web site. http://www.massgeneral.org/neurosurgery/services/faq_transsphenoidalsurgery_cushingdisease.aspx. Accessed April 13, 2013.
- Cortisol level. MedlinePlus Web site. http://www.nlm.nih.gov/medlineplus/ency/article/003693.htm. Updated December 11, 2011. Accessed April 15, 2013.
- Cushing's syndrome/disease. American Association of Neurological Surgeons Web site. http://www.aans.org/en/Patient Information/Conditions and Treatments/Cushings Disease.aspx. Accessed April 13, 2013.
- Cushing's syndrome. http://endocrine.niddk.nih.gov/pubs/cushings/cushings.aspx#diagnosis. National Endocrine and Metabolic Diseases Information Service Web site. Accessed April 13, 2013.