It is important that the diagnosis of Cushing's syndrome is confirmed. First a doctor will test you for Cushing's syndrome. Once glucocorticoid medicines have been ruled out, there are 4 types of tests that are generally used to find out if you have Cushing's syndrome. These tests measure the amount of cortisol in samples of urine, blood, or saliva to determine how much cortisol is circulating in your body. If the tests show that the level of cortisol is too high, it means you have Cushing's syndrome.1 If the test is not positive for high levels of cortisol, then signs and symptoms should be closely watched. If your symptoms get worse, check back with your doctor in 6 months.1
In certain cases, doctors recommend specific types of tests based on a person's medical history. Some of these recommendations are included below.
|Special recommendations for Cushing's syndrome diagnostic testing1|
|If you …||UFC test||Late-night
|Are taking medicine for seizures (for example, phenobarbital, phenytoin, or carbamazepine)||Yes||Yes||No|
|Have kidney failure||No||*||Yes|
(1 mg overnight)
|Have an adrenal mass||No||Yes||Yes|
(1 mg overnight)
UFC=urine-free cortisol; DST=dexamethasone suppression test; *=No recommendation stated.
Following are brief descriptions of tests that are used to diagnose Cushing’s syndrome. However, complete information about these tests, along with instructions for patients, should be obtained from your doctor.
(Note: The longer DST is considered more accurate in determining whether high cortisol levels are caused by Cushing’s syndrome or some other condition.1)
If a patient is diagnosed with Cushing’s syndrome after measuring the level of cortisol in his or her body, the next step is additional testing to diagnose if the cause of excess cortisol is Cushing’s disease (a pituitary tumor) or a different form of Cushing’s syndrome.1
*MRI=magnetic resonance imaging; CT=computerized tomography.
If a pituitary tumor is suspected but not found on MRI, it may be because either the tumor is too small to see, or it is not a pituitary tumor, but rather an ACTH-producing tumor in another part of the body. Additional imaging and/or tests are then needed.2
Once the doctor knows what is causing the level of cortisol to be too high, then he or she can determine the most appropriate treatment.
References: 1. Nieman LK, Biller BMK, Findling JW, et al. The diagnosis of Cushing’s syndrome: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2008;93:1526-1540. 2. Newell-Price J, Bertagna X, Grossman AB, Nieman LK. Cushing’s syndrome. Lancet. 2006;367:1605-1617. 3. The Hormone Foundation’s patient guide to the diagnosis of Cushing’s syndrome. The Hormone Foundation. http://www.hormone.org/resources/patient_guides/upload/mgmt-cushings-syndrome-070609.pdf. Accessed August 4, 2009. 4. Arnaldi G, Angeli A, Atkinson AB, et al. Diagnosis and complications of Cushing’s syndrome: a consensus statement. J Clin Endocrinol Metab. 2003;88:5593-5602. 5. Nieman LK, Ilias I. Evaluation and treatment of Cushing’s syndrome. Am J Med. 2005;118:1340-1346.