Dexamethasone Suppression Test

Indications

Screen/diagnose Cushing’s syndrome.

Procedure

The test is done in the outpatient setting.

  1. The patient takes dexamethasone 1 mg at bedtime (around 11 pm).
  2. Cortisol level is measured at 8 to 9 am the morning after taking dexamethasone.

Interpretation

Cortisol level after dexamethasone:

Caveats

Inducers, rapid dexamethasone metabolism Inhibitors, slow dexamethasone metabolism
Phenobarbital, Phenytoin, Carbamazepine, Primidone Aprepitant/fosaprepitant
Rifampin Rifapentine Ethosuximide Itraconazole
Pioglitazone Ritonavir
Fluoxetine
Diltiazem
Cimetidine

See this list of a CYP inducers and inhibitors.

Alternatives

References