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. Glucagon-sensitive adenylate cyclase was found in pheochromocytomas but not in a functional 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.
D000262:Adenylyl Cyclases / Q000378:metabolism; D000310:Adrenal Gland Neoplasms / Q000175:diagnosis*; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D004837:Epinephrine / Q000097:blood; D005189:False Positive Reactions; D005260:Female; D005934:Glucagon; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010673:Pheochromocytoma / Q000175:diagnosis*; D011674:Pulse / Q000187:drug effects
D005934:Glucagon; D000262:Adenylyl Cyclases; D009638:Norepinephrine; D004837:Epinephrine