Dexamethasone suppression test

From WikiLectures

Hypothalamic-Pituitary-Adrenal axis

Basic test for suspected Cushing's syndrome.

Principle of the test: Inhibition test based on the principle of negative feedback. The application of a synthetic glucocorticoid (dexamethasone, DEX) physiologically leads to the suppression of the ACTH-cortisol axis and therefore to a decreased secretion of both hormones. In patients with Cushing's syndrome (whether primary or secondary), this response is insufficient.

The Dexamethasone test has several variations. The most frequently used is the short „overnight“ test during which a single dose is administered in the evening (1 mg or 2 mg per os). In the morning, the levels of ACTH and Cortisol before and after the administration of DEX are compared.

An alternative is the six-day dexamethasone test during which a low dose (2 mg) is followed by a high dose (8 mg) of DEX. Normally, the Hypophysis and Adrenal glands respond even after administering a low dose of DEX. In patients with central Cushing's syndrome (Pituitary adenoma) the suppression occurs only after a high dose of DEX. If there's no reaction, another type of Cushing's syndrome has to be considered – peripheral or paraneoplastic Cushing's syndrome.

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Original text is from WikiSkripta – Dexametazonový supresní test

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