Clonidine-Suppression Test. A Useful Aid in the Diagnosis of Pheochromocytoma

Evaluation of the clonidine suppression test in the diagnosis of phaeochromocytoma

“…False-negative results may theoretically occur if the tumour has intermittent secretory activity, as measurement of the plasma catecholamines at the various time points may refer to different states of biochemical activity. 8 Our series has shown this as not to be a major problem. If it does become such, the problem may be overcome by measuring levels of catecholamine metabolites, the metanephrines.…”

“…Tests were positive if criterion 1: plasma noradrenaline 42.96 nmol l -1 at 3 h post-clonidine; 8 criterion 2: plasma noradrenaline plus adrenaline 42.96 nmol l -1 at 3 h post-clonidine or a baseline plasma adrenaline plus plasma noradrenaline 411.82 nmol l -1 ; 9 criterion 3: plasma noradrenaline 42.96 nmol l -1 at 3 h after clonidine and o50% fall in noradrenaline compared with basal level at 3 h post-clonidine. 10 …”

“…These include acute clonidine withdrawal, acute alcohol withdrawal, vasodilator therapy with hydralazine or minoxidil, acute myocardial ischaemia or infarction, acute cerebral vascular accident, cocaine abuse, acidosis, hypoglycaemia, hypotension in shock and severe congestive heart failure. 8 Diet can also contribute to falsepositive result. For example, caffeic acid, a catechol found in coffee, is known to interfere with the assays of plasma catecholamines.…”

“…The clonidine suppression test was introduced by Bravo et al 8 to address the problems outlined above. It is based on the principle that clonidine suppresses normal neurogenically mediated catecholamine release, but does not affect autonomous tumour production of catecholamines.…”

“…Several criteria have been proposed for interpretation of the test in order to achieve maximum sensitivity and specifity. [8][9][10] These are set out in Methods.…”