Clinical Chemistry Blog Notes 32B

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Dexamethasone Suppression Test

--- has been employed as a means of assessing cortisol production in depressed patients and as a potential diagnostic tool for identifying the possible cause of depression. A patient with Cushing's syndrome has high percentage in experience in severe depression.

Procedure

1. Administration of 1.0 mg dexamethasone orally at 11 p.m
2. Samples for plasma cortisol measurement are collected the following day at 4 p.m and 11 p.m.
* * * there is no special patient preparation * * *

- if either the 4 p.m of the 11 p.m sample shows a total cortisol level greater than 5.0 ug/dL the test is considered positive of endogenous depression.
- a rise in the 4 p.m value above the 5.0 ug/dL cutoff is termed early escape a strong degree of resistance to suppression of cortisol synthesis by dexamethasone.

Normal Results

Cortisol levels should decrease after you receive dexamethasone.

Low dose:

• Overnight: 8 a.m. plasma cortisol <>

High dose:

• Overnight: > 50% reduction in plasma cortisol

Clinical Situation Dexamethasone

• Hyperplasia 50% supprresion

• Adrenal tumor no suppression

• Ectopic ACTH production no suppression
  

Reference: Clinical Chemistry book pages 413- 429 By: Bishop
Clinical Chemistry book pages 332