The value of the clonidine‐suppression test in the diagnosis of pheochromocytoma

We assessed the clinical value of a clonidine‐suppression test in the diagnosis of pheochromocytoma. Three different groups were investigated: group I, 10 patients with operatively verified catecholamine‐secreting tumors (1 extra adrenal paraganglioma); group II, 34 patients with “neurogenic” hypertension; and group III, 14 normotensive, healthy subjects. Clonidine, 300μg given orally at time zero, significantly reduced mean systolic/diastolic blood pressure (MBP) in all 3 groups: group I, maximum MBP fall ‐19/0 mm Hg; group II, ‐43/21 mm Hg; and group III, ‐25/9 mm Hg, respectively. The maximal MBP fall was seen between 2 and 3 hours after administration of clonidine. Mean plasma concentrations of noradrenaline/norepinephrine (NA) decreased in groups II and III, in group II from 2.6±0.3 to 0.7±0.05 nmol/l (p<0.001), and in group III from 1.3±0.2 to 0.6±0.06 nmol/l, respectively. Plasma concentrations of adrenaline/epinephrine (A) were low < 0.2 nmol/l and remained unchanged during the test. In contrast, in patients with pheochromocytoma (group I), NA and A mean plasma concentrations were high before clonidine, 7.7±2.2 nmol/l for NA and 4.0±1.7 nmol for A, and remained high or somewhat elevated during the 3 hours of observation. No patient showed a decrease in plasma catecholamines during the test. After successful operation for the catecholamine‐secreting tumors, all 10 patients achieved normal BP (mean 135/83 mm Hg supine) and had normal basal plasma catecholamine concentrations (NA 2.8± 0.5 nmol/l, A<0.2 nmol/l) with normal suppression of NA after clonidine to 1.1± 0.2 nmol/l (p<0.01 compared with basal values). We conclude that the clonidine‐suppression test is a safe and simple diagnostic method for verification or exclusion of pheochromocytomas, especially in patients with normal resting (baseline) catecholamine levels (4 patients in the present study). No significant or clinically relevant side effects were noted during the test apart from some sedation and dry mouth.