Function tests

• Suspicion of pheochromocytoma in case of borderline urine-catecholamine findings and/or elevated plasma-catecholamine metabolites metanephrine and normetanephrine, but no more than a minimum of three times the upper norm.
• The test is only applicable for basally increased plasma-catecholamine values.

Bradycardia, hypovolemia, hypotension, current treatment with beta-blockers

Clonidine is an alpha-adrenergic agonist, which centrally attacks and suppresses especially noradrenalin, and to a lesser degree adrenalin.  In case of pheochromocytoma, the increase of catecholamines is caused by autonomous secretion, which cannot be suppressed by clonidine administration.

Adrenalin, noradrenalin, blood pressure monitoring

3 ml EDTA-blood has to be centrifuged straight away, the plasma transferred into a special tube for catecholamine evaluation (+ glutathione) and frozen immediately.  

Blood collection before and 3 hours after clonidine administration. Mark tubes with extraction timings. A freezing container will be issued on request. During the test, blood pressure and pulse should be checked every 30 min.

The following medication should be discontinued 7 days before test start:  Tricyclic antidepressants, phenoxybenzamine, doxazosin, MAO-inhibitors, paracetamol, levodopa and beta-blockers.

Apart from calcium-antagonists, any other antihypertensive therapy has to be paused at least 24 hours prior to test start.

• 30 min prior to test start, insert indwelling venous line. The patient should be empty-stomached.
• First blood collection in supine position, after a 30 min rest, for evaluation of adrenalin and noradrenalin. Blood pressure and pulse checks.
• Oral administration of 300 µg Clonidine (i.e. Catapresan®).
• Further blood collection after 3 hours for adrenalin and noradrenalin evaluation.

Side effects
Severe drop in blood pressure in healthy persons. Following clonidine administration, driving ability is reduced.

After clonidine administration, the plasma-catecholamines should fall to normal values or decrease by at least 40% of the original value.