L C Pinto1, C K Kramer2, J L Camargo3, L H Canani3, J L Gross3, C B Leitão3. 1. Endocrine Division, Hospital de Clínicas de Porto Alegre, Rua Ramiro Barcelos 2350, Prédio 12, 4° Andar, Porto Alegre, RS, 90035-003, Brazil. lanacfp@gmail.com. 2. Division of Endocrinology, Department of Medicine, University of Toronto, Toronto, Canada. 3. Endocrine Division, Hospital de Clínicas de Porto Alegre, Rua Ramiro Barcelos 2350, Prédio 12, 4° Andar, Porto Alegre, RS, 90035-003, Brazil.
Abstract
BACKGROUND: Urinary metanephrine is a reliable method to estimate catecholamine secretion. Traditionally, urinary metanephrines are collected into chilled containers containing hydrochloric acid (HCl) and most laboratories freeze urinary samples before analysis. It is uncertain if these pre-analytic procedures alter metanephrine values. AIM: To evaluate if acidifying and freezing urine samples affect the accuracy of urinary metanephrine measurements. METHODS: Random urine samples from healthy individuals were collected. Urine samples were distributed into two containers: with HCl 50% homogenized with urine to obtain pH < 2, and without HCl. Each container was divided again into aliquots for immediate measurement or freezing. One aliquot with acid (group 1) and another without acid (group 2) were sent immediately to the laboratory for testing (HPLC), while the other two aliquots, one with acid (group 3) and another without it (group 4) were frozen for 3 months at - 20 °C. Bland-Altman's test was used to analyze inter-assay agreement between measurements. RESULTS: A total of 15 individuals were included (mean age 27.5 ± 5.9 years, 8 male and 14 white). No difference was observed on mean urinary metanephrine/creatinine ratio between groups: group 1: 0.23 ± 0.11, group 2: 0.22 ± 0.07, group 3: 0.25 ± 0.13, group 4: 0.25 ± 0.15 mg/g creatinine; P > 0.05 for all the comparisons). Bland-Altman's analysis showed agreement between the standard method (group 1) and the experimental method (group 4). CONCLUSION: Measurement of urinary metanephrines by HPLC method is not influenced by sample acidification nor freezing at - 20 °C for 3 months.
BACKGROUND: Urinary metanephrine is a reliable method to estimate catecholamine secretion. Traditionally, urinary metanephrines are collected into chilled containers containing hydrochloric acid (HCl) and most laboratories freeze urinary samples before analysis. It is uncertain if these pre-analytic procedures alter metanephrine values. AIM: To evaluate if acidifying and freezing urine samples affect the accuracy of urinary metanephrine measurements. METHODS: Random urine samples from healthy individuals were collected. Urine samples were distributed into two containers: with HCl 50% homogenized with urine to obtain pH < 2, and without HCl. Each container was divided again into aliquots for immediate measurement or freezing. One aliquot with acid (group 1) and another without acid (group 2) were sent immediately to the laboratory for testing (HPLC), while the other two aliquots, one with acid (group 3) and another without it (group 4) were frozen for 3 months at - 20 °C. Bland-Altman's test was used to analyze inter-assay agreement between measurements. RESULTS: A total of 15 individuals were included (mean age 27.5 ± 5.9 years, 8 male and 14 white). No difference was observed on mean urinary metanephrine/creatinine ratio between groups: group 1: 0.23 ± 0.11, group 2: 0.22 ± 0.07, group 3: 0.25 ± 0.13, group 4: 0.25 ± 0.15 mg/g creatinine; P > 0.05 for all the comparisons). Bland-Altman's analysis showed agreement between the standard method (group 1) and the experimental method (group 4). CONCLUSION: Measurement of urinary metanephrines by HPLC method is not influenced by sample acidification nor freezing at - 20 °C for 3 months.
Authors: Jacques W M Lenders; Karel Pacak; McClellan M Walther; W Marston Linehan; Massimo Mannelli; Peter Friberg; Harry R Keiser; David S Goldstein; Graeme Eisenhofer Journal: JAMA Date: 2002-03-20 Impact factor: 56.272
Authors: Jacques W M Lenders; Quan-Yang Duh; Graeme Eisenhofer; Anne-Paule Gimenez-Roqueplo; Stefan K G Grebe; Mohammad Hassan Murad; Mitsuhide Naruse; Karel Pacak; William F Young Journal: J Clin Endocrinol Metab Date: 2014-06 Impact factor: 5.958