Corticotropin releasing hormone CRH test

Investigation Protocol

Indications

To help distinguish between ACTH dependent Cushing’s syndrome of ectopic and pituitary causes.

Preparation and precautions

Patients should be fasting from midnight (water only). Patients should bring all their usual medication with them to take after the test and for documentation. Estrogen containing medications, including the contraceptive pill and hormone replacement therapy, should be stopped for six weeks prior to measuring serum cortisol. This is because estrogen induces cortisol binding globulin and leads to elevations in measured serum cortisol. Any steroid containing medications should also be avoided, as they may interfere with the hypothalamo-pituitary-adrenal axis, or cross react with the cortisol assay.

Allergic reactions, flushing and hypotension have been described after ovine CRH and so the test must only be performed with full medical support present, although human CRH is now in wide usage.

Procedure

Insert a cannula gauge 20 with a three-way tap, and using a syringe or the vacutainer connector system, fill one plain clotted bottle for cortisol, and one EDTA tube for ACTH. This forms the t= -15 minute sample. Both tubes need to be labelled, then the EDTA tube centrifuged, separated and frozen before transport to the laboratory.

Repeat this basal sampling after 15 minutes, and label t= 0 minutes.

Administer 100mcg intravenous human CRH via a separate indwelling cannula.  

Repeat the sampling at 15, 30, 45, 60, 90 and 120 minutes. Mark the patient’s details, date and time of samples on each bottle: t= +15, +30 and so on. After each sample, flush the cannula with 2mls 0.9% sodium chloride. Before each subsequent sample is taken, withdraw 2mls of blood and discard to remove any trace of the sodium chloride flush.

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Patient information sheet

Corticotropin releasing hormone CRH test 

Your doctor has asked us to coordinate a blood test to measure some very specialised hormones. This involves us giving you an injection of a hormone, and then taking a series of blood samples to see how your body responds to it. The purpose of this is to help us to find out if your pituitary gland is causing an imbalance of steroid hormones in your body, known as Cushing’s disease.

Please have nothing to eat from 11pm the night before the test. Please bring all your usual medication with you, which we will document and which you can take at the end of the test. Please come to the unit at 9am on the morning of the test. 

You will be given an injection of a hormone through a small tune in the back of your hand or arm. This may cause you to feel a 'flushing sensation' for a few seconds, though other reactions are very unusual. A series of blood samples are then taken over a period of approximately two hours. 

If you have diabetes, this test may cause a temporary rise in your blood glucose levels for a few days after the test. The nurse looking after you during the test will advise you about what to do if this happens.

The test takes two hours from the time the injection is given so please allow at least two and a half hours to be in the unit. You will be resting in a reclining chair and you may eat and drink as normal after the test.

You may wish to bring a book or magazine to read. We do have a radio, or you can access Patientline; alternatively you may like to bring your own personal radio/cd player (please bring your own headphones). You may bring someone to stay with you during the test but there is not enough space for more than one person.

Children are discouraged, as this can be disruptive to other patients. However, if this poses a particular problem for you please discuss this with the senior nurse in the unit. You should be able to undertake normal activities after the test is finished and it should not interfere with your ability to drive home.

If you have any problems or queries about the test please contact:

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