What is clonidine suppression test?

Clonidine suppression test is type of test in order to try and exclude the diagnosis of phaeochromocytoma in patients with hypertension and borderline changes in plasma catecholamines or urinary catecholamine metabolites.

Clonidine is a medication used for treating hypertension. It works on the brain to decrease the “sympathetic tone”, that is, the intensity of nerve signals to the adrenal medulla. Clonidine suppresses the release of catecholamines and metanephrines from normal adrenal medulla.

Why is clonidine suppression test performed?

There are a couple of reasons why the clonidine suppression test may be done:

  • To determine if elevated basal levels of plasma catecholamines are due to an idiopathic hyperadrenergic state or to pheochromocytoma.
  • Elevated plasma metanephrines and/or catecholamines, less than four times the upper limit of normal for the given test, in patients with suspected pheochromocytoma or paraganglioma.
  • Test is not indicated in patients with unequivocally positive plasma or urine biochemical test for pheochromocytoma (catecholamines, metanephrines, VMA).
  • Test is not necessary in patients with normal baseline plasma free metanephrine and normetanephrine (excludes pheochromocytoma).


What should I know before receiving clonidine suppression test?

The Clonidine suppression test should never be considered as a “gold standard” for the diagnosis. It is just one of the tests that help diagnosing pheo. Moreover, the results of the clonidine suppression test can be confusing too. Catecholamines and metanephrines may be trending toward different directions. Some markers may be even higher after clonidine. The test is not needed for most patients. Even in the patient who should benefit most from it.


How to prepare for clonidine suppression test?

It is advisable that there are a great number of things that need preparing before the test, including:

  • Discontinue interfering medications 1-5 days prior to test: diuretics, tricyclic antidepressants, beta blockers
  • Patient fasting for 10 hours overnight prior to test.
  • Relax while doing the test
  • Quiet environment

What happens during clonidine suppression test?

  • Subjects supine throughout the entire test period with an indwelling

i.v. for blood sampling and i.v. fluids as required.

  • Baseline blood pressure and heart rate measured 3 times and recorded in the data collection sheet.
  • Baseline blood sample taken after 30 minutes of supine rest and immediately before administration of clonidine.
  • Blood pressure and heart rate monitored continuously with single measurements recorded in the data collection sheet at 1 hour and 2 hours post clonidine.
  • Test blood sample taken at 3 hours (180 minutes) after clonidine, with time of the blood sample recorded in the data collection sheet.
  • Blood pressure and heart rate are measured and recorded in triplicate in the data collection sheet, immediately after the 3-hour test blood sample is drawn.
  • Blood samples must be transported to the laboratory immediately after collection of the final 3-hour test sample

What happens after clonidine suppression test?

Very little chance of a problem from having a blood sample taken from a vein can occur.

Firstly, you may get a small bruise at the site. However, you can lower the chance of bruising by keeping pressure on the site for several minutes.

In some rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. You should use a warm compress several times a day to solve this situation

Moreover, ongoing bleeding can be a problem for some patients with bleeding disorders. Some medications such as aspirin, warfarin (Coumadin), and other blood-thinning medicines are able to make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Explanation of results

What do my results mean?

Your test is called normal if:

  • Fall in plasma norepinephrine to the normal range
  • Decrease in plasma norepinephrine to less than 50% of baseline value
  • Fall in plasma total catecholamines (Epi, NE and DA) to normal range (500 pg/mL or less)
  • Fall in plasma normetanephrine to the normal range
  • Decrease in plasma normetanephrine by 40% from baseline value

However, changes in plasma epinephrine and metanephrine are variable, and thus non-diagnostic for pheochromocytoma using this test

Previous controversy centered on the various definitions of a positive test.  For example, hypertensive patients without pheochromocytoma and with normal or near normal baseline norepinephrine levels may fail to suppress by 50% (false positive).  Conversely, patients with pheochromocytoma and near normal baseline norepinephrine may suppress to the normal range (false negative).  These issues appear to have been resolved with the use of normetanephrine, and exclusion of testing in patients with normal baseline plasma free metanephrines.


Please discuss with your doctor any questions you may have about your test results.




Hello Health Group does not provide medical advice, diagnosis or treatment.


Review Date: September 8, 2017 | Last Modified: September 8, 2017

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