Clonidine Test For Phaeochromocytoma
The diagnosis of phaeochromocytoma should initially be tested with two 24h urine collections. The clonidine test will only be required if there is strong clinical suspicion and borderline elevations of catecholamine excretion.
Medical anti-hypertensive therapy is not contra-indicated for this test but since there is a trend to lower the urinary excretion of (nor-) adrenaline, it is ideal to refrain from their use for 24h prior to and during the test. The laboratory should be contacted to avoid the use of any drugs which interfere with the analytical detection of catecholamines.
Physiological catecholamine secretion is suppressed by clonidine whereas autonomous secretion by a tumour is not suppressed.
Since clonidine may produce a profound fall in blood pressure, the subject should remain lying in bed throughout the night (2100-0700h) except to pass urine.
Patients should be admitted to hospital and should refrain from smoking or consuming caffeine (eg tea, coffee and Cola drinks)
- 0.3 mg clonidine
- two 24h urine containers with acid preservative
Day 1: 2100h patient should empty his/her bladder and start an overnight collection of urine from 2100 to 0700h. Use collection bottles with acid preservative.
Day 2: 2100h patient should empty his/her bladder
Immediately afterwards 0.3mg clonidine should be orally administered .
An overnight collection of urine should be made from 2100-0700h. Use collection bottles with acid preservative.
In subjects both with and without hypertension, the effect of sleep and clonidine should lower
urinary noradrenaline < 58 nmol/mmol creatinine
urinary adrenaline < 18 nmol/mmol creatinine
Phaeochromocytoma should be considered in any patients with higher values.
Macdougall IC, Isles CG, Stewart H, Ingles GC, Finlayson J, Thomson I, Lees KR, McMillan NC, Morley P, Ball SG. Overnight clonidine suppression test in the diagnosis and exclusion of pheochromocytoma. Am J Med 1988;84:993-1000.