Dexamethasone Suppression Test – Low Dose for ACTH
Test Name: Dexamethasone Suppression Test – Low Dose for ACTH
Sample Type: Serum
Purpose: Evaluates the regulation of cortisol production and helps assess suspected Cushing syndrome (hypercortisolism).
What is the test?
The Low-Dose Dexamethasone Suppression Test (LDDST) checks whether cortisol production can be appropriately suppressed by dexamethasone, a synthetic glucocorticoid.
Why is it done?
- Screening for Cushing syndrome
- Evaluation of excessive cortisol production
- Helps assess abnormal hypothalamic-pituitary-adrenal (HPA) axis activity
- May be used alongside ACTH and cortisol measurements to determine the underlying cause
How is it performed?
A low dose of dexamethasone is administered, usually at night, followed by measurement of serum cortisol the next morning. The exact dose and timing should follow the laboratory/physician protocol.
Interpretation
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Adequate cortisol suppression: Generally argues against endogenous Cushing syndrome.
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Failure to suppress cortisol: May indicate hypercortisolism and requires further clinical evaluation.
Results should be interpreted along with ACTH, clinical findings, medications, and other endocrine investigations.
Important: Certain medications, estrogen therapy, alcohol use, stress, and other conditions can influence test results. The test should be performed strictly according to the physician's instructions.
