Diagnosis of Cushing's syndrome

Diagnosis of Cushing's syndrome

Seek Expert Advice.

Who should be tested

Testing for Cushing's syndrome is recommended in the following groups (1):

• Patients with unusual features for age (e.g. osteoporosis, hypertension)

• Patients with multiple and progressive features, particularly those who are more predictive of Cushing's syndrome

• children with decreasing height percentile and increasing weight
  
  

• patients with adrenal incidentaloma compatible with adenoma

The following tests are advised NOT to be used to test for Cushing's syndrome (1)

• random serum cortisol or plasma ACTH levels

• urinary 17-ketosteroids

• insulin tolerance test

• loperamide test

• tests designed to determine the cause of Cushing's syndrome (e.g. pituitary and adrenal imaging, 8 mg DST)

For the initial testing for Cushing's syndrome, one of the following tests based on its suitability for a given patient, is recommended (1):

• urine free cortisol (UFC; at least two measurements)

• late-night salivary cortisol (two measurements)

• 1-mg overnight dexamethasone suppression test (DST)

• longer low-dose DST (2 mg/d for 48 h)

Diagnostic criteria that suggest Cushing's syndrome are UFC greater than the normal range for the assay, serum cortisol greater than 1.8 mug/dl (50 nmol/liter) after 1 mg dexamethasone (1-mg DST), and late-night salivary cortisol greater than 145 ng/dl (4 nmol/liter).

Subsequent evaluation based on expert advice

Reference:

• Nieman LK et al. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline.J Clin Endocrinol Metab. 2008 May; 93(5): 1526-1540.