Overnight Dexamethasone Test: What Is the Cortisol Question?

If you expected an ordinary blood test, being given medicine to take the night before can feel confusing. Ask the endocrine team to explain what the test is checking and how the two parts fit together.

What does “suppression” mean here?

The test checks whether the body can appropriately switch off cortisol production. Cambridge University Hospitals describes it as part of investigating or excluding Cushing’s disease. The question is about cortisol regulation, not whether a set of symptoms proves a diagnosis.¹

Ask: “What concern prompted this test in my case, and what will the result help you decide?” Keep the answer beside the referral details rather than trying to infer it from the test name.

Why is the morning appointment arranged first?

CUH instructs patients to book the next morning’s blood test before taking the prescribed evening tablets. The sample’s timing matters for interpretation. The blood sample measures cortisol after dexamethasone, linking the evening medicine with the following morning’s result.¹

Confirm the exact medicine instructions and blood-test time with your own service. If the appointment is cancelled or the instructions are unclear, contact the endocrine team before proceeding. Ask what to do if you miss the prescribed time rather than inventing a replacement schedule.

What if I take HRT, contraception or steroids?

CUH identifies estrogen-containing oral HRT or combined contraception, and steroids in tablets, creams, sprays or inhalers, as medicines that can affect interpretation. The endocrine team must clarify the plan for your products. If contraception is paused, alternative protection is needed. Possible pregnancy requires discussion before proceeding.¹

Send the team the names and routes of everything you use. Ask them to confirm in writing what to take, what to omit if necessary and when to resume any paused prescription. Do not stop prescribed steroids or hormone treatment on your own to prepare for the test.

Does the result finish the investigation?

CUH says the endocrine consultant reviews the result. Further testing may be requested and explained, and a clinic discussion may follow. The specialist nurse advises when to restart medicines that were paused for the test.¹

Before leaving the arrangements settled, ask when you should hear from the service and whom to contact if that message has not arrived. Bring any difficulty completing the planned sequence to the result discussion so the clinician knows what happened.

My Body Changed. Now What? includes a Visit Brief. Use it to organize your referral question, medicine questions and result arrangements alongside the endocrine team’s instructions. See the book.