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High-dose dexamethasone suppression test
Synonym(s): HDDST
Overview
- A high dose of dexamethasone inhibits pituitary ACTH secretion through negative feedback and hence this decreases plasma [cortisol]
.
Uses
Alone
- To differentiate adrenal-dependent hyperadrenocorticism (ADH) from pituitary-dependent hyperadrenocorticism (PDH) after hyperadrenocorticism Hyperadrenocorticism has been diagnosed by screening tests.
- Cannot be used to diagnose spontaneous or iatrogenic hyperadrenocorticism or to monitor trilostane Trilostane therapy.
- Not necessary in dogs with hyperadrenocorticism if the low dose dexamethasone suppression test Low dose dexamethasone suppression test shows adequate suppression at 4 h.
Sampling
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Tests
Availability
- [Cortisol] widely available at many commercial laboratories.
Validity
Sensitivity
- Around 25% of pituitary tumors Pituitary adenoma will not show suppression.
Specificity
- Some pituitary tumors (macroadenomas?) respond like adrenal tumors (do not suppress).
Technique intrinsic limitations
- Plasma cortisol levels do not suppress in 25% 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 ACTH assay.
- Ultrasound Ultrasonography: adrenal gland.
Result Data
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Further Reading
Publications
Refereed papers
- Recent references from VetMedResource 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 PubMed.