No influence of antihypertensive agents on plasma free metanephrines

Background: Hypertension can be the predominant sign of pheochromocytoma (PCC) and sympathetic paraganglioma (sPGL) and screening for PCC/sPGL is often performed in patients who are already being treated with antihypertensive agents. There is very little information about the influence of antihypertensive drugs on plasma free metanephrines. The aim of this study was to determine whether commonly prescribed antihypertensive drugs can falsely elevate plasma free metanephrines concentrations measured by LC-MS/MS analysis.

Methods: In a prospective study we included patients with newly diagnosed hypertension, who started monotherapy with an antihypertensive agent (i.e. beta-blocker, thiazide diuretic or angiotensin-converting enzyme (ACE) inhibitor). Plasma free metanephrine (MN) and normetanephrine (NMN) levels were measured before and one month after the start of the medication quantified by LC-MS/MS.

Results: Between 2009 and 2014, 39 patients were included (beta-blocker n = 13, thiazide diuretic n = 14 and ACE inhibitor n = 12). In the whole group, the median plasma free MN and NMN concentrations at baseline were 0.19 [0.17-026] nmol/L and 0.56 [0.38-0.95] nmol/L. One month after the start of antihypertensive treatment, the median plasma free MN and NMN concentrations were comparable; 0.20 [0-16-0.24] nmol/L and 0.63 [0.39-0.75] nmol/L, respectively (P = 0.43 and P = 039). Separate analysis for each of the three antihypertensive agents examined did not reveal any significant changes in the median plasma free MN and NMN concentrations.

Conclusions: The measurement of plasma free MN and NMN with LC-MS/MS is not affected by use of beta-blockers, diuretics and ACE inhibitors. Withdrawal of these drugs prior to the quantification of plasma metanephrines is therefore not necessary. (C) 2016 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.