Cushing's Disease Diagnosis
In the case of Cushing's disease, diagnosis usually involves determining if the patient's body is producing excess levels of the hormone cortisol. If so, the doctor then typically calls for further tests to determine the cause of the excess cortisol. Tests used to make a help make a Cushing's disease diagnosis may include urinary tests, imaging scans, and a petrosal sinus sampling test.
In order to make a Cushing's disease diagnosis, the doctor will usually ask a number of questions about:
- The patient's medical history
- His or her current symptoms
- Whether there is a family history of any medical problems
- Any medicines the patient is taking.
The doctor will also likely perform a physical exam, looking for any signs of Cushing's disease. If these suggest Cushing's disease, then the doctor will order more tests.
Testing for Cushing's disease generally involves a two-step process. First, doctors perform tests to see if there is too much cortisol in the body. If so, then they order tests to see if a pituitary adenoma is causing the excess cortisol. If a pituitary adenoma is causing the excess cortisol, then the doctor diagnoses Cushing's disease; if the excess cortisol is being caused by another condition (see Cushing's Syndrome Causes), then the disorder is known as Cushing's syndrome.
Tests used for diagnosing Cushing's disease can include:
- A 24-hour urinary free cortisol level test
- Dexamethasone suppression test
- CRH (corticotropin-releasing hormone) stimulation test
- Imaging tests
- Petrosal sinus sampling.
24-Hour Urinary Free Cortisol Level
To make a Cushing's disease diagnosis, the 24-hour urinary free cortisol level is the most specific diagnostic test available. The patient's urine is collected over a 24-hour period and tested to determine the level of cortisol in it. Levels higher than 50 to 100 micrograms a day for an adult suggest either Cushing's syndrome or Cushing's disease. The normal upper limit varies in different laboratories, depending on which measurement technique is used.
Once doctors have diagnosed Cushing's disease, they generally use other tests to determine 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 performed.