Dexamethasone Suppression Test

Diagnostic Use

The Dexamethasone suppression test is used to assess the hypothalamic-pituitary-adrenal axis by measuring cortisol response to dexamethasone administration. Failure of cortisol suppression indicates autonomous cortisol production and warrants further investigation.
Dexamethasone is a potent, synthetic corticosteroid that does not interfere with the Roche cortisol assay.

Low dose (1 mg) dexamethasone is taken orally at 23:00 hours and blood is taken for cortisol measurement at 8:00am the following morning.

Department

Endocrinology Lab

Delphic Registration Code

CORT

Laboratory Handling

Phlebotomy

Please label with collection time.

Registration

Check this is the dexamethasone suppression test and not a request for dexamethasone testing itself

Constituent Tests

• Cortisol – serum/plasma

Synonyms

Overnight Suppression Test
DST

Turnaround Time

3 days

Specimen Type

• Serum
• Plasma

Specimen Requirements

Tube/Container Type:

Preferred

• Serum (Red Cap)

Pre-testing Requirements

All corticosteroid therapy must be withdrawn prior to commencing this test.

Aliquot Instructions

Sample Type

• Serum
• Plasma

Minimum Volume (ml)

0.1

Transport to Lab

Ambient (8 - 24 degrees Celsius)
Frozen

Interpretation

For post dexamethasone samples, the following clinical cut offs and their respective comments are used:

DEX1 ≤49 nmol/L – Cushing’s syndrome is virtually excluded.

DEX2 50-100 – Cushing’s syndrome cannot be excluded. Follow up with a 24-hour urine cortisol. Consider referral to a clinical endocrinologist.

DEX3 >100 – Further investigation of hypercortisolism and referral to a clinical endocrinologist is warranted.

Test Method

Roche Cortisol II ECLIA

Non-Funded Test Cost

$39.64 (Exclusive of GST)

Billing Code

9407

Contact Information

Enquiry Form

Contact Information

Enquiry Form