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Cushing's syndrome is a rare hormonal disorder that occurs when the body produces excessive levels of cortisol for an extended period of time. Certain tests can help determine if excess levels of cortisol are present and, if so, why. Testing for Cushing's syndrome may involve a special urinary test, tests that help determine the kind of tumor that is causing the excess cortisol, and imaging tests.

Cushing's Syndrome Testing: An Overview

In order to make a Cushing's syndrome diagnosis, the doctor will usually ask a number of questions and perform a physical exam. If the doctor suspects a person has Cushing's syndrome, he or she will typically order certain tests. Cushing's syndrome testing helps to determine if excess levels of cortisol are present and why.
These tests can include:
  • A 24-hour urinary free cortisol level test
  • Dexamethasone suppression test
  • CRH stimulation test
  • Dexamethasone-CRH test
  • Petrosal sinus sampling
  • Imaging tests.

24-Hour Urinary Free Cortisol Level Test

When performing Cushing's syndrome testing, the 24-hour urinary free cortisol level test is the most specific diagnostic test used. The patient's urine is collected over a 24-hour period and tested for the amount of cortisol. Levels higher than 50 to 100 micrograms a day for an adult suggest Cushing's syndrome. The normal upper limit varies in different laboratories, depending on which measurement technique is used.
Once a doctor has diagnosed Cushing's syndrome, he or she will usually order other tests to find the exact location of the abnormality that is leading to excess cortisol production. The choice of test depends, in part, on the preference of the endocrinologist or the center where the test is being performed.
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Last reviewed by: Arthur Schoenstadt, MD
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