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Low dose overnight dexamethasone suppression test

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Why do I need this test?

Your doctor has recommended that you take this test to help with the diagnosis and the management of your condition. Please would you read this carefully and ask us about anything that is not clear or if you would like more information.

What is the purpose of the test?

This test will help us to know if you might have Cushing’s syndrome. Cushing’s syndrome is a disease caused by excess cortisol production. Cortisol is a natural steroid hormone or chemical signal. It is produced by the adrenal glands, which are just above the kidneys, in response to instructions from the pituitary gland, which is a small gland beneath the brain. This test is also recommended as a routine investigation if you have a benign adrenal nodule (adrenal adenoma).

How long will the test take?

We will ask you to take a tablet at home at night, and then attend for a single blood test the following morning.

Who will carry out the test?

A nurse or phlebotomist (a health care professional trained to take blood) will take the blood test.

What will I have to do?

Your endocrinologist will give you a prescription for one dexamethasone tablet (1 mg) and a blood request form. You will need to collect the tablet from your pharmacy. You should take the tablet at 11pm at home, and then attend for a blood test to be taken at 9am the following morning. The timing of the tablet and the blood test is very important and needs to be as close to the recommended times as possible so that the results are accurate.

Is any drug or medicine used during the test?

Dexamethasone is a steroid tablet that reduces the production of cortisol (the natural steroid hormone).

What will happen during the test?

We will do one blood test.

What are the possible risks or side-effects of the test?

Long-term dexamethasone treatment has many possible side-effects, but a single dose is very unlikely to have any side-effects at all. If you have any concerns, please contact the endocrine specialist nurse.

What are the alternatives to the test?

It can be difficult to diagnose Cushing’s syndrome. A number of different tests may be necessary, including blood tests, urine tests and scans. This varies from patient to patient, and depends on the results of your investigations. Your endocrinologist will advise you about this in more detail.

What will happen after the test?

We will send your blood samples to the laboratory for analysis. When your results are available, either the endocrine specialist nurse or your endocrinologist will discuss these with you. This will usually be at your next clinic appointment. They will advise you about other tests you might need.

Who do I contact if I have any questions?

Endocrine Specialist Nurses

Royal Sussex County Hospital
Endocrine specialist nurse
01273 696955 extension 64379

Princess Royal Hospital, Haywards Heath
Endocrine specialist nurse
01444 441881 extension 65660

If you have any urgent or emergency questions then your GP can advise you or they will contact the hospital on your behalf.

Patient self-help groups and further information: The Pituitary Foundation

This information is intended for patients receiving care in Brighton & Hove or Haywards Heath.

The information in this leaflet is for guidance purposes only and is in no way intended to replace professional clinical advice by a qualified practitioner.

Publication Date: July 2021

Review Date: April 2024

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