How do healthcare providers diagnose Cushing syndrome?

Diagnosing Cushing syndrome can be complex and difficult. This syndrome is easier to recognize once it develops fully, but healthcare providers try to diagnose and treat it before it gets to that point. No single test can definitively diagnose the condition, so healthcare providers often use several steps to diagnose Cushing syndrome. If you are being checked for Cushing syndrome, the tests may occur in the following order1,2:

Your healthcare provider will ask about all medications and other treatments you have taken to see whether any of them could be responsible for raising your cortisol levels. Make sure you include everything you take, including joint or nerve injections received for pain; “tonics,” dietary supplements, and herbal medications; nasal sprays; progesterone; and skin creams (including bleaching agents).1

A laboratory will check to see whether your cortisol levels are normal. This test might be one of the following:

Urine cortisol test

Urine is collected for 24 hours.

Late-night salivary cortisol test

A special device is used for collecting saliva late at night. You can mail the sample to a laboratory or deliver it to your healthcare provider.

Dexamethasone suppression test

For this test, you take dexamethasone, a drug that suppresses or stops cortisol production, by mouth, and then your blood level of cortisol is measured. The test may be done overnight or across 3 days.3

If your results are not normal, your healthcare provider may do further tests or refer you to an endocrinologist, a healthcare provider who specializes in hormones and hormone disorders, for the tests. These tests might include:

  • Another test from Step 2
  • Serum midnight cortisol test, which measures the amount of cortisol in your blood late at night
  • Dexamethasone-suppressed corticotropin-releasing hormone (Dex-CRH) test, which can help determine the cause of the symptoms

If your cortisol levels are still above normal and you receive a diagnosis of Cushing syndrome, your healthcare provider will check for the cause. Tests to find the cause might include the following:

  • A CRH stimulation test, which involves a series of blood samples
  • A high-dose dexamethasone suppression test, a variation on the dexamethasone suppression test described earlier
  • Magnetic resonance imaging (MRI) or other imaging to see the glands that might be causing symptoms
  • Petrosal sinus sampling, which is a blood test that measures levels of ACTH coming from the pituitary gland

Certain medical conditions can make some of the tests listed earlier unsafe or ineffective, so your healthcare provider may not use the tests. These conditions can include:

  • Pregnancy
  • Epilepsy
  • Renal failure
  • Cyclic Cushing syndrome, in which cortisol is sometimes normal and sometimes high

In addition, several kinds of medications unrelated to Cushing syndrome may interfere with test results. Make sure your healthcare provider knows about every drug you are taking before testing for Cushing syndrome.1

Citations

  1. Nieman, L. K., Biller, B. M. K., Findling, J. W., Newell-Price, J., Savage, M. O., Stewart, P. M., & Montori, V. M. (2008). The diagnosis of Cushing’s syndrome: An Endocrine Society clinical practice guideline. Retrieved March 2, 2017, from https://academic.oup.com/jcem/article/93/5/1526/2598096 
  2. Boscaro, M., & Arnaldi, G. (2009). Approach to the patient with possible Cushing’s syndrome. Journal of Clinical Endocrinology and Metabolism, 94(9), 3121–3131. Retrieved April 9, 2019, from https://www.ncbi.nlm.nih.gov/pubmed/19734443
  3. MedlinePlus. (n.d.). Dexamethasone suppression test. Retrieved March 2, 2017, from https://medlineplus.gov/ency/article/003694.htm
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