Canis ISSN: 2398-2942

High-dose dexamethasone suppression test

Contributor(s): David Bruyette

Overview

  • A high dose of dexamethasone inhibits pituitary ACTH secretion through negative feedback and hence this decreases plasma [cortisol] Endocrinology: hypopituitary adrenal axis - diagram.

Sampling

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Tests

Availability

  • [Cortisol] widely available at many commercial laboratories.

Validity

Sensitivity

  • Good for identifying pituitary tumors.

Specificity

  • Some pituitary tumors (macroadenomas?) respond like adrenal tumors (do not suppress).

Technique (intrinsic) limitations

  • [Plasma cortisol] do not suppress in 15% of PDH cases probably because ACTH is released from the pars intermedia rather than the pars distalis and the pars intermedia is less sensitive to the negative feedback of high [plasma cortisol].
  • Does not differentiate adrenocortical adenomas from adrenocortical carcinomas.
  • Failure to suppress requires additional testing:
    • ACTH assay.
    • Ultrasound.

Result Data

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Feldman E C, Nelson R W & Feldman M S (1996) Use of low- and high-dose dexamethasone tests for distinguishing pituitary-dependent from adrenal tumor hyperadrenocorticism in dogs. JAVMA 209, 772-775.


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