High dose dexamethasone suppression test
SPEG (Scottish Paediatric Endocrine Group)
No special preparations are required.
Drug(s) Given
Dexamethasone tablets available as 500 microgram tablets.
Give 2mg every 6 hours for as total of eight doses.
In younger children give 80 micrograms/kg/dose every 6 hours for a total of eight doses.
Maximum single dose is 2mg.
How Given
Orally on day two of the test.
Timing of Administration
After basal urine and blood samples have been taken.
| Time | Action |
| Day 1 @ 09:00 | Take venous blood sample. Start 24 hour urine collection. |
| Day 1 @ midnight | Take venous blood sample. |
| Day 2 @ 06:00, 12:00, 18:00, 00:00 | Take oral dexamethasone 6 hourly |
| Day 3 @ 06:00, 12:00, 18:00, 00:00 | Take oral dexamethasone 6 hourly |
| Day 4 @ 06:00 | Take venous blood sample. Start 24 hour urine collection. |
| Time | |||
| Day 1 @ 09:00 | Cortisol | ACTH | Urine steroids |
| Day 1 @ midnight | Cortisol | ACTH | |
| Day 4 @ 06:00 | Cortisol | ACTH | Urine steroids |
In Pituitary-dependent hypercortisolism (Cushing’s disease), the plasma cortisol concentration usually suppresses to at least 50% of basal values.
In approximately 10% of patients with Cushing’s disease there is a failure to suppress cortisol.
Approximately 10% of patients with ectopic ACTH secretion will suppress.
It is important to discuss the use of dexamethasone suppression and the interpretation of the results with a paediatric endocrinologist.