Pathology Handbook

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Dexamethasone Suppression test

Alternative Names:

DST
Overnight DST

Laboratory:

Clinical Biochemistry

Test Code:

CORT

Specimen Types:

Blood

Container Types:

Lithium Heparin (with Gel)
SST

Collection & Request Instructions:

Requesting doctor must arrange for patient to take1mg Dexamethasone at 11pm the night before blood collection.

An early morning cortisol (preferably between 8 - 9am) must be collected the following morning.

Transport Instructions between Sites and/or Laboratories:

Room Temperature

Assay Frequency:

Daily

Additional Notes:

A morning cortisol of < 50 nmol/L after 1 mg dexamethasone administered overnight indicates normal suppression of the hypothalamic pituitary adrenal axis. Levels >/= 50 nmol/L may indicate hypercortisolism.

Please note that hospitalised inpatients not infrequently have an abnormal 1mg dexamethasone suppression test response. If possible, investigations should be delayed until acute illness has subsided.