The clonidine supression test with measurement of plasma metanephrines by enzyme immunoassay
Peter Kentos1, Anna Moravcikova2, Peter Vanuga1, Miroslava Michalekova2, Alexander Kreze3 & Mikulas Pura1
Background: In pheochromocytomas, the measurement of fractionated metanephrines is the first-line test for diagnosis and the false-positive results remain a problem. Among various parameters and tests used, only the suppression of normetanephrine provides reliable evidence that a pheochromocytoma is not present.
Objective: Aim of the study was to analyse the role of clonidine suppression test in laboratory diagnosis of pheochromocytoma.
Subjects and methods: Clonidine tests were carried out in 201 patients, 13 with and 188 without the tumor. The presence of pheochromocytoma was confirmed by histology and the absence by a disease-free extended follow-up. Plasma fractionated metanephrines (expressed as median, 5th and 95th percentile) were measured by an enzyme immunoassay (EIA) at baseline, 2 and 3 h after administration of clonidine.
Results: All tests performed were uneventful in all subjects. Clonidine decreased plasma normetanephrine in patients without pheochromocytoma from 63 (30; 120) at baseline to nadir 39 (14; 79). Plasma metanephrine concentrations (at baseline 36 (15; 92)) showed variable responses to clonidine (nadir 39 (14; 79)). Percent decreases in plasma normetanephrine after clonidine varied from 076%, and on average were similar to those of metanephrine (68±57 vs 61±35%), which varied from 0 to 88%. In contrast, in patients with pheochromocytoma, plasma concentrations of metanephrines remained unchanged normetanephrine 797 (108; 4067) at baseline, and nadir 620 (101;3088), respectively metanephrine in the basal state 123 (38; 603) and nadir 125 (31; 322).
Conclusions: The results obtained thus suggest clonidine suppression testing is worthwhile in the diagnosis of pheochromocytoma by blood tests. Clonidine suppressive test is valuable tool in diagnostic of adrenal medullary hyperfunction. The procedure is safe and technically non-complicated. Moreover, EIAs in analysis of metanephrines could be used comparable to more expensive and and widely available HPLC method in metanephrines analyses.