Cushing's syndrome laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Furqan M M. M.B.B.S[2]


When Cushing's syndrome is suspected, either a dexamethasone suppression test (administration of dexamethasone and frequent determination of cortisol and ACTH level) or a 24-hour urinary measurement for cortisol offer equal detection rates. Dexamethasone is a glucocorticoid and simulates the effects of cortisol, including negative feedback on the pituitary gland. When dexamethasone is administered and a blood sample is tested, high cortisol would be indicative of Cushing's syndrome. A novel approach, recently cleared by the US FDA, is sampling cortisol in saliva over 24 hours, which may be equally sensitive, as late night levels of salivary cortisol are high in Cushingoid patients. Other pituitary hormone levels may need to be ascertained.

Laboratory Findings

The laboratory findings associated with Cushing's syndrome are:[1]

Diagnosis of hypercortisolism

Hypercortisolism can be established by any of the following tests:

Tests to establish the cause of hypercortisolism

Approach to the diagnosis of Cushing's syndrome

24 hr urine cortisol or midnight salivary cortisol shows hypercortisolism
Measure serum ACTH
ACTH independent Cushing syndrome
Corticotrophic releasing hormone (CRH) (desmopressin) test
ACTH dependent Cushing syndrome
Adrenal CT/MRI
Evaluate as ACTH independent Cushing syndrome if NO ACTH response
Evaluate as ACTH dependent Cushing syndrome if there is an ACTH response
Corticotrophic releasing hormone (CRH) (desmopressin) AND high dose dexamethasone suppression test OR MRI brain
Adequate stimulation and suppression OR pituitarty mass >6mm
Mixed/negative response OR no pituitary mass OR mass < 6mm
Cushing disease
Inferior petrosal sinus sampling
Cushing disease if step-up in ACTHEctopic ACTH secretion if no step-up in ACTH

Other Laboratory findings

  • Hypokalemia


  1. Raff H, Findling JW. A physiologic approach to the diagnosis of the Cushing's syndrome. Ann Intern Med 2003;138:980-91. PMID 12809455

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