Dexamethasone suppression test

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Dexamethasone suppression test
Diagnostics
Dexamethasone structure.svg
proopiomelanocortin derivatives
POMC
     
γ-MSH ACTH β-lipotropin
         
  α-MSH CLIP γ-lipotropin β-endorphin
       
    β-MSH  

The dexamethasone suppression test (DST) is a blood test that assesses adrenal gland function by measuring how cortisol levels change in response to an injection of dexamethasone.[1] It is typically used to diagnose Cushing's syndrome.

Physiology[edit]

Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary to suppress the secretion of ACTH. Specifically, dexamethasone binds to glucocorticoid receptors in the pituitary gland, which lies outside the blood brain barrier, resulting in regulatory modulation.[2]

Interpretation[edit]

Low-dose and high-dose variations of the test exist.[3]

The test is given at low (usually 1–2 mg) and high (8 mg) doses of dexamethasone and the levels of cortisol are measured to obtain the results.[1]

A low dose dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production. A high dose dexamethasone exerts negative feedback on pituitary ACTH producing cells but not on ectopic ACTH producing cells or adrenal adenoma.

Low-dose[edit]

A normal result is a decrease in cortisol levels upon administration of low-dose dexamethasone. Results indicative of Cushing's disease involve no change in cortisol on low-dose dexamethasone, but inhibition of cortisol on high-dose dexamethasone. If the cortisol levels are unchanged by low- and high-dose dexamethasone then other causes of Cushing's syndrome must be considered with further work-up necessary.

High-dose[edit]

After the high-dose dexamethasone, it may be possible to make further interpretations.[4]

ACTH† Cortisol Interpretation
Undetectable or low is not suppressed by high or low doses. Primary Hypercortisolism is likely.
Normal to elevated is not suppressed by high or low doses Ectopic ACTH syndrome is likely. If an adrenal tumor is not apparent, a chest CT and abdominal CT is indicated to rule out a different tumor secreting ACTH.
High is not suppressed by low doses, but is suppressed by high doses Cushing's disease should be considered. This is because the pituitary still retains some feedback control. A pituitary MRI would be needed to confirm.

†ACTH as measured prior to dosing of dexamethasone[5]

Equivocal results should be followed by a CRH stimulation test, with Inferior petrosal sinus sampling.

References[edit]

  1. ^ a b Medline Plus "Dexamethasone suppression test"
  2. ^ Cole MA, Kim PJ, Kalman BA, Spencer RL (February 2000). "Dexamethasone suppression of corticosteroid secretion: evaluation of the site of action by receptor measures and functional studies". Psychoneuroendocrinology 25 (2): 151–67. doi:10.1016/S0306-4530(99)00045-1. PMID 10674279. 
  3. ^ Isidori AM, Kaltsas GA, Mohammed S, et al (November 2003). "Discriminatory value of the low-dose dexamethasone suppression test in establishing the diagnosis and differential diagnosis of Cushing's syndrome". J. Clin. Endocrinol. Metab. 88 (11): 5299–306. doi:10.1210/jc.2003-030510. PMID 14602765. 
  4. ^ Kumar, Abbas, Fausto. Robbins and Cotran Pathologic Basis of Disease, 7th ed. Elsevier-Saunders; New York, 2005
  5. ^ Longo, Dan L.; Fauci, Anthony S.; Kasper, Dennis L.; Hauser, Stephen L.; Jameson, J. Larry; Loscalzo, Joseph (2012), Harrison's Principles of Internal Medicine (18th ed.), McGraw Hill Medical, pp. 2897–2898, ISBN 978-0-07174889-6