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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.
This test will help us to know if you 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.
The test will take about two hours. We will ask you to take some tablets at home for two days before the test.
The test will be carried out by an Endocrine Specialist Nurses.
We will give you a prescription for eight dexamethasone tablets (0.5 mg each). You should start taking these at 12:00 noon, two days before the test, at the following times:
Two days before the test: 12pm (noon); 6pm; 12am (midnight)
One day before the test: 6am; 12pm (noon); 6pm; 12am (midnight)
Morning of the test: 6am
The timing of when you take these tablets is very important so that the results are accurate. It needs to be as close to the recommended times as possible.
We will ask you to come to the hospital for the test at 7.30am in the morning after you have taken the last dexamethasone tablet.
We will give you eight dexamethasone tablets. Dexamethasone is a steroid tablet that reduces the production of cortisol (the natural steroid hormone). You will also be given an injection of CRH. This is a natural hormone (chemical signal) produced by the hypothalamus. The hypothalamus is part of the brain which controls hormone function by signalling to the pituitary gland. CRH stimulates cortisol production. Measuring how your hormones respond to the dexamethasone and the CRH will help us to know if you have Cushing’s syndrome.
We will check your weight so that we know the correct dose of CRH to give to you. A nurse will use a needle to put a small plastic tube into a vein in your arm. We will use this to take blood samples and to give you an injection without the need for any more needles. After we have taken the first blood sample, we will give you an injection of CRH. Over the next hour we will measure your response to the test by taking more blood samples. After we have completed the test, you will be able to go home.
Long-term dexamethasone treatment has many possible side-effects, but this short course of dexamethasone tablets is very unlikely to have any side-effects. If you have diabetes, you may find that your blood sugars are higher than usual whilst you are taking the dexamethasone tablets. If you have any concerns, please contact the endocrine specialist nurse.
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.
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.
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