Clonidine suppression test

Investigation Protocol


Exclusion of phaeochromocytoma in patients with hypertension and mild elevations of urinary and serum metanephrines (<4xULN) in whom no other explanation has been found. 

Preparation and precautions

The referring doctor needs to have stopped all alpha and beta blocking agents 48 hours prior to the test. Patients should also be warned to avoid paracetamol,tricyclic antidepressants such as amitryptiline and diuretics for 5 days prior to the test. Frail patients, or those with coronary heart disease or episodes of hypotension or collapse should not undergo this test. Warn the patient that they will experience a drop in blood pressure during the test. Warn the laboratory that they will be receiving multiple samples for analysis of metnephrines.


The patient should be assessed by a doctor on arrival to rule out hypovolaemia and confirm that their medication has been adjusted appropriately.

The patient should then be admitted to a quiet darkened room to minimise sympathetic stimulation. Insert a cannula gauge 20 with a three-way tap into one arm.Document pulse and BP three times every 5 minutes, and every 30 minutes thereafter. Ask the patient to rest.

After 30 minutes, take blood for baseline catecholamines and metanephrines (Lithium heparin and EDTA tubes) and label them -5minutes. Repeat after 5 minutes and label 0minutes. All samples will need to be placed on ice and spun at 4C and frozen until assayed. Administer 0.3mg clonidine orally.

Continue pulse and BP recording every 30 minutes, as hypotension will usually occur. Dramatic and symptomatic falls in BP may be treated with leg elevation or iv fluids if necessary. Take further samples for catecholamines and metanephrines at 60, 120 and 180 minutes. Continue monitoring the patient every 30 minutes until their BP normalises and the patient feels fully recovered. The cannula can then be removed, and the patient offered a meal and can go home.

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Patient information sheet

Clonidine suppression test

Your doctor has referred you for a clonidine suppression test to rule out a condition called Phaeochromocytoma.

If you are taking any of the following medications, please contact us as you will require special instructions on stopping them for a few days before this test: alpha blockers such as doxasosin or alfusosin; beta blockers such as atenolol, bisoprolol, metoprolol, propranolol; amitryptiline, paracetamol and diuretics such as bendorflumethaside or furosemide.

You can eat and drink and take your other tablets as normal on the day of the test, but smoking should be avoided on the day of the test.

Before the test, you will be asked to lie down and rest in a darkened room. During the test blood samples will be taken 5 times over a three hour period. To allow this to happen easily with the minimum of discomfort for you, we will be inserting a small tube (a cannula) into a vein in your arm at the start of the test. After resting for half an hour, some baseline samples of blood will be taken. You will then be given a tablet of clonidine, which is likely to drop your blood pressure, and some people will feel rather dizzy following this. We will then take further samples of blood and closely monitor your pulse and blood pressure. By 3 hours, the test will be complete, but you will be asked to rest until you feel completely back to normal and your blood pressure has recovered. You will then be offered a meal and allowed to go home. Most people have completely recovered by the end of the test, and so it is not necessary for someone else to drive you to and from the appointment unless you want them to. You should expect your stay at the hospital to last at least four and a half hours.

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. 

If you have any queries about the test, please contact

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