Endocrine Division, Hospital de Clínicas de Porto Alegre, Rua Ramiro Barcelos 2350, Prédio 12, 4° Andar, Porto Alegre, RS, 90035-003, Brazil.
Division of Endocrinology, Department of Medicine, University of Toronto, Toronto, Canada.
J Endocrinol Invest. 2020 Jan;43(1):53-56. doi: 10.1007/s40618-019-01076-9. Epub 2019 Jun 21.
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.
To evaluate if acidifying and freezing urine samples affect the accuracy of urinary metanephrine measurements.
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.
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).
Measurement of urinary metanephrines by HPLC method is not influenced by sample acidification nor freezing at - 20 °C for 3 months.
尿中甲肾上腺素是一种可靠的方法来估计儿茶酚胺的分泌。传统上，尿中甲肾上腺素被收集到含有盐酸（HCl）的冷藏容器中，大多数实验室在分析前将尿液样本冷冻。目前尚不确定这些分析前的程序是否会改变甲肾上腺素的值。
评估酸化和冷冻尿液样本是否会影响尿中甲肾上腺素测量的准确性。
随机收集健康个体的尿液样本。将尿液样本分为两部分：一部分与 50%HCl 均匀混合，使尿液 pH 值<2，另一部分不加 HCl。每个容器再分成等分试样，用于立即测量或冷冻。一份加酸（第 1 组），另一份不加酸（第 2 组）立即送往实验室进行测试（HPLC），而另两份，一份加酸（第 3 组），另一份不加酸（第 4 组）在-20°C 下冷冻 3 个月。采用 Bland-Altman 检验分析测量之间的组内一致性。
共纳入 15 名个体（平均年龄 27.5±5.9 岁，8 名男性，14 名白人）。各组间尿中甲肾上腺素/肌酐比值的平均值无差异：第 1 组：0.23±0.11，第 2 组：0.22±0.07，第 3 组：0.25±0.13，第 4 组：0.25±0.15mg/g 肌酐；所有比较的 P 值均>0.05）。Bland-Altman 分析显示标准方法（第 1 组）与实验方法（第 4 组）之间存在一致性。
通过 HPLC 方法测量尿中甲肾上腺素不受样本酸化或-20°C 冷冻 3 个月的影响。
