Low-dose dexamethasone suppression test

LDDST

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Overview

  • Endocrinology: hypopituitary adrenal axis - diagramFig.1 Endocrinology: hypopituitary adrenal axis - diagram
    Administration of exogenous glucocorticoid (dexamethasone) suppresses hypothalamic-pituitary axis   (Fig. 1)  .
  • Natural cortisol levels are suppressed for >8 hours in normal animal.
  • Animals with hyperadrenocorticism show breakthrough of suppression by 8 hours.
    Wider range of degree and duration of suppression in cats than dogs.

Uses

In combination

Other points

  • Has a number of disadvantages over ACTH stimulation test   
  • Affected by more variables.
  • Takes 8 hours to complete.

Result data

Normal (reference) values

  • [Plasma cortisol] = <50% of [basal cortisol] at 2-4 hours and failure to escape suppression by 8 hours (most cases).

Abnormal values

  • Hyperadrenocorticism: [cortisol] fails to suppress or escapes suppression by 8 hours.

Errors and Artifacts

  • Stress: must be minimized.
  • No sedation possible.
  • Recent administration of exogenous glucocorticoids may suppress the hypothalamic-pituitary axis.
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