Quantification of Unconjugated Metanephrines in Human Plasma without Interference by Acetaminophen

Abstract

Background: Pheochromocytoma is a rare cause of hypertension resulting from increased catecholamine secretion. We aimed to develop a method to measure unconjugated plasma normetanephrine (NMN) and metanephrine (MN) without interference from acetaminophen, a widely prescribed drug for headaches. Methods: Plasma samples were obtained from 48 subjects (23 males, 25 females; mean age, 49 ± 14 years; hypertension, n = 37) under resting conditions. Following extraction on solid-phase cation-exchange columns, unconjugated metanephrines were analyzed by HPLC with electrochemical detection and with 4-hydroxy-3-methoxybenzylamine as an internal standard. Catecholamines were measured by HPLC. Results: The assays were linear up to 2000 pg for NMN and for MN. Intraassay imprecisions (CVs) were 4.7% for NMN and 7.0% for MN, and the interassay CV was 12% for both NMN and MN. The limit of detection was 11 fmol for NMN and 17 fmol for MN. Ingestion of acetaminophen or its addition to plasma did not interfere with the MN peaks. Plasma NMN and MN were positively correlated (r = 0.52 and 0.49, respectively; P <0.01 for both) with the respective catecholamines. Plasma NMN (r = 0.27; P = 0.02) but not MN positively correlated with age, whereas only plasma catecholamines (and not metanephrines) were positively correlated (P <0.05) with diastolic blood pressure. Conclusions: This sensitive MN assay is not affected by simultaneous acetaminophen medication, and reveals a correlation of metanephrines with plasma and urinary catecholamines and age but not with blood pressure.

Exercise induces excessive normetanephrine responses in hypertensive diabetic patients

“…High-performance liquid chromatography (HPLC) was used for the determination of plasma unconjugated metanephrines [14]. The intraassay coefficients of variation (CV) were < 5% (normetanephrine) and 7% (metanephrine), interassay CVs were < 12·5%.…”

“…The intraassay coefficients of variation (CV) were < 5% (normetanephrine) and 7% (metanephrine), interassay CVs were < 12·5%. Plasma catecholamines were analyzed by reverse-phase HPLC [15] using plasma extraction tubes (ESA, Bedford, MA) for the isolation procedure [14]. Interassay and intraassay CVs were < 5% for both compounds.…”

Increased prevalence of heterozygous 21‐OH germline mutations in patients with adrenal incidentalomas

“…Pheochromocytoma and Cushing's syndrome were excluded by determination of urinary excretion of catecholamines and an overnight dexamethasone suppression test, respectively. To rule out hormonal hypersecretion, urinary catecholamine excretion was measured by HPLC (Raber et al, 2000;Roden et al, 2001), while plasma concentrations of cortisol, 17-OHP, testosterone, aldosterone and renin were determined by radioimmunoassays, as described previously (Waldhäusl & Lewandowsky, 1973;Herkner et al, 1978;Waldhäusl et al, 1978;Vierhapper et al, 1988). Based on the clinical development of all patients included in the study none of the patients harboured a malignant tumour.…”

Using free plasma metanephrines in the diagnosis of pheochromocytoma

“…Pomocí metodiky HPLC-ECD ("high performance liquid chromatography with electrochemical detection" -detektor Coulochem II /ESA Biosciences, Inc.; Chelmsford, MA, USA/) byly u pacientÛ vy‰etfieny metanefriny v plazmû. (8)(9)(10)(11)(12)(13)(14) Krev byla odebírána po 30minutovém zklidnûní na lÛÏku po pfiedchozí kanylaci periferní Ïíly do zkumavky s EDTA, do 30 min stoãena plazma v chlazené centrifuze (4 °C) a následnû zmraÏena pfii -80 °C. Postup byl na v‰ech praco-vi‰tích provádûn podle standardního protokolu.…”