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Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary gland to suppress the secretion of adrenocorticotropic hormone (ACTH). Specifically, dexamethasone binds to glucocorticoid receptors in the anterior pituitary gland, which lie outside the blood–brain barrier , resulting in regulatory modulation.
Two dexamethasone suppression tests (DSTs) are generally used, the overnight test and the 48 hour test. [8] For both tests, a plasma cortisol level above 50 nmol/L is indicative of Cushing's disease. [8] However, 3–8% of patients with Cushing's disease will test negative due to a retention of dexamethasone suppression abilities. [8]
[2] [3] Dexamethasone should be used as the corticosteroid of choice in these cases as it is the only corticosteroid that will not affect diagnostic test results. [2] [29] To confirm inappropriately low cortisol secretion, testing can include baseline morning cortisol level in the blood or morning cortisol level in the saliva. [2]
A fluid or water deprivation test is a medical test [1] which can be used to determine whether the patient has diabetes insipidus as opposed to other causes of polydipsia (a condition of excessive thirst that causes an excessive intake of water). The patient is required, for a prolonged period, to forgo intake of water completely, to determine ...
The ACTH test (also called the cosyntropin, tetracosactide, or Synacthen test) is a medical test usually requested and interpreted by endocrinologists to assess the functioning of the adrenal glands' stress response by measuring the adrenal response to adrenocorticotropic hormone (ACTH; corticotropin) or another corticotropic agent such as tetracosactide (cosyntropin, tetracosactrin; Synacthen ...
Dexamethasone is a fluorinated glucocorticoid medication [10] used to treat rheumatic problems, a number of skin diseases, severe allergies, asthma, chronic obstructive pulmonary disease (COPD), croup, brain swelling, eye pain following eye surgery, superior vena cava syndrome (a complication of some forms of cancer), [11] and along with antibiotics in tuberculosis. [10]
In each case the fetal sex can be determined quickly, and if the fetus is a male the dexamethasone can be discontinued. If female, fetal DNA is analyzed to see if she carries one of the known abnormal alleles of the CYP21 gene. If so, dexamethasone is continued for the remainder of the pregnancy at a dose of about 1 mg daily. [201]
Evocative/suppression testing refers to a class of tests performed where one substance is measured both before and after the administration of another substance to determine if the levels are stimulated ("evocative") or suppressed.
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