Dexamethasone (8 mg) is taken orally between 11 pm and midnight, and a single blood sample is drawn at 8 am the next day for measurement of serum cortisol.
With this protocol, the 8 am serum cortisol concentration is <5 Ž ¼g/dL in most patients with Cushing disease (i.e., a pituitary tumor) and is usually undetectable in normals.