Dexamethasone CRH 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.

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.