SPEG (Scottish Paediatric Endocrine Group)
To identify Cushing’s Syndrome.
The Overnight Dexamethasone Suppression Test is used as an initial screening test.
Overnight dexamethasone suppression test
No specific preparation required.
Ensure the patient is not taking steroids in any form.
Drug(s) Given
Dexamethasone 10 micrograms per kg body weight up to a maximum of 1 mg.
Available as scored 500 microgram tablets.
Round the dose to the dearest 250 micrograms (i.e. half a tablet).
How Given
Orally in tablet form.
Timing of Administration
Give the dose of dexamethasone between 23:00 and midnight.
| Time (minutes) | Action |
| 23:00 to 00:00 | Give dexamethasone orally. |
| 09:00 next day | Take blood sample. |
| Time | |
| 09:00 | Cortisol |
In normal subjects, the morning plasma cortisol concentration is suppressed to less than 50 nmol/l.
In patients with Cushing’s syndrome, such marked suppression is not observed.
Patients taking hepatic enzyme-inducing drugs (e.g. phenytoin, phenobarbitone) may have false negative results.