Glucagon and clonidine testing in the diagnosis of pheochromocytoma.

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Abstract
We assessed the sensitivity and specificity of glucagon stimulation and clonidine suppression tests in the diagnosis of pheochromocytoma in 113 hypertensive patients, 39 with and 74 without the tumor. In the glucagon stimulation test, blood was sampled 2 minutes after intravenous injection of 0.28 mumol (1 mg) glucagon, and in the clonidine suppression test, blood was sampled 3 hours after administration of oral clonidine, 1.30 mumol (0.3 mg)/70 kg body wt. Baseline levels of catechols in antecubital venous blood were abnormal, with norepinephrine greater than 7.10 nmol/l (1,200 pg/m), epinephrine greater than 1.51 nmol/l (276 pg/ml), norepinephrine/dihydroxyphenylglycol (DHPG) ratio greater than 1.09, or dopa greater than 35.53 nmol/l (7,000 pg/ml), in 30 of 39 patients with pheochromocytoma (sensitivity 77%) and 1 of 74 patients without pheochromocytoma (specificity 99%). Results of the glucagon test were abnormal (norepinephrine greater than 11.83 nmol/l [2,000 pg/ml] or more than threefold increase fr...