Evaluation of Endocrine Tests. C: glucagon and clonidine test in phaeochromocytoma

The diagnosis of phaeochromocytoma is based on the demonstration of catecholamine excess. Urine and plasma metanephrine measurements are highly sensitive tests for the diagnosis of phaeochromocytoma, but moderate elevations in metanephrines lack optimal specificity. In this study we aimed to evaluate the diagnostic value of additional tests, i.e. glucagon stimulation and clonidine suppression test, in patients with moderately elevated catecholamines and/or metanephrines.

Patients with suspected phaeochromocytoma with moderately elevated catecholamines and/or metanephrines in plasma or urine were subjected to the glucagon stimulation and clonidine suppression test. The presence of phaeochromocytoma was confirmed by histology and the absence by a disease-free extended follow-up.

Fifty-five patients were included. Phaeochromocytoma was diagnosed in 11 patients. The follow-up period in patients without phaeochromocytoma was 56 (19 to 154) months. The sensitivity of the glucagon test was 30% and the specificity 100%. The clonidine test had no discriminative power, because the area under the ROC curve was not significantly different from 0.5.

The clonidine suppression test without normetanephrine measurements and the glucagon stimulation test are not sensitive enough to safely exclude phaeochromocytoma in patients with mildly elevated plasma or urine catecholamines.