Dexamethasone Suppression Test

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Contents 1 Indications 2 Reference-interval 3 Principle 4 Procedure 5 Interferences 6 Notes 7 More General Terms 8 Additional Terms 9 References

Indications

• diagnosis of Cushing's syndrome

Reference-interval

• serum cortisol < 3 ug/mL

Principle

• Dexamethasone suppresses pituitary secretion of ACTH which, in turn, suppresses endogenous secretion of cortisol.
• cortisol assays do NOT detect dexamethasone
  

• Predictive value of a positive test is poor (0.6%)
• Predictive value of a negative test is close to 100%.

Procedure

• dexamethasone: 1 mg at 11 PM
• serum cortisol at 8 AM

Interferences

• False positives occur with:
• physiologic stress, psychologic stress
• renal failure
• estrogen therapy
• pharmaceutical agents

• phenytoin
• phenobarbital
• carbamazepine
• rifampin

• endogenous depression
• incorrect timing of dexamethasone administration or of blood sampling
• significant obesity
• alcoholism
• anorexia nervosa

Notes

• 8 mg dexamethasone suppression test if 1 mg dexamethasone suppression test is negative

• serum cortisol suppresses with ACTH-secreting pituitary adenoma
• serum cortisol does not suppress with ectopic ACTH-secreting tumor

More General Terms

• provocative clinical test

Additional Terms

• cortisol in serum
• dexamethasone (Decadron, Maxidex, AK-Dex, Ozurdex)

References

1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 652
2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, American College of Physicians, Philadelphia 1998, 2006

dexamethasone suppression test