A laboratory workup is performed for individuals with signs and/or symptoms compatible with Cushing's syndrome. Tests include:
24-hour urinary free cortisol level: This is the most specific diagnostic test. The patient will collect urine over a 24-hour period. An elevated urinary cortisol level suggests Cushing's syndrome. Usually, this test needs to be repeated several times for confirmation.
1 mg overnight dexamethasone suppression test: In this test, the patient takes 1 mg of dexamethasone and a fasting cortisol is drawn at 8 a.m. the next day. If the blood cortisol level is not suppressed, Cushing's syndrome is suggested.
Late night salivary cortisol test: In this test, cortisol values in saliva are measured. Between 11 p.m. and midnight, the patient places a cotton swab in the mouth, and then places the moist cotton into a tube. An elevated salivary cortisol late at night may suggest the presence of Cushing’s syndrome.
Other testing to determine the cause of Cushing’s syndrome may be done for each individual.
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