Suppression or urine. The 2 screening tests that can be performed are an overnight Dexamethasone suppression test (odst) or a 24 hour urine collection for cortisol. For the odst, you take Dexamethasone (a steroid) the night before you get blood drawn for a morning cortisol. The normal response to taking dex is a decrease in cortisol production. If one of these tests is abnormal, a 2 day dex test is done to confirm.