Clonidine suppression test


5 mL blood in lithium heparin tube.


Plasma Normetadrenaline, LC-MS/MS.

  1. The patient must be relaxed and comfortable in bed.

  2. A venous cannula inserted.

  3. After 30 minutes (to allow patient to settle after venepuncture) a baseline specimen for plasma catecholamines is collected.

  4. The patient is given 300 µg clonidine hydrochloride orally.

  5. Blood for catecholamines is collected at 180 minutes.

  6. The cannula is removed and the patient checked for fitness to leave the centre; drowsiness is a possible side effect.

Reference Interval:

Plasma normetadrenaline level should drop to 40% of baseline level, or to within the reference interval.


Diagnosis of Phaeochromocytoma, when other investigations are equivocal. May be replaced by Free metanephrines (plasma).


Failure to suppress plasma normetadrenaline indicates autonomous release from a tumour.


Eisenhofer G J Clin Endocrinol Metab. 2003 Jun;88(6):2656-66