Basis of false‐positive glucagon tests for pheochromocytoma

In more than half of 67 patients suspected of having pheochromocytoma, glucagon stimulation increased plasma free norepinephrine (NE) and epinephrine (E) 50% or more, with rising blood pressure or pulse rate; only three patients, however, harbored a pheochromocytoma. A low degree of catecholamine conjugation accounts for most of the false‐positive results. In patients with low conjugated NE + E there was a greater rise in free NE + E and free E as well as in pulse rate after glucagon stimulation than in those with normal levels of conjugated NE + E. Glueagon‐sensuive adenylate cyclase was found in pheochromocytomas but not in afunctional adrenocortical adenomas. After sham administration of glucagon, there were rises in blood pressure but not in free NE or E in four patients. The glucagon‐induced catecholamine test can be false‐positive in hyperadrenergic essential hypertensive patients with abnormally low conjugated NE + E. Saline alone in a sham glucagon test in susceptible patients raises systolic blood pressure and pulse rate, and therefore, if plasma free NE and E are measured and found not to rise this type of false‐positive result can be eliminated. Clinical Pharmacology and Therapeutics (1981) 29, 687–694; doi: 10.1038/clpt.1981.96