Validation of single measurement of 12-hour urine excretion for estimation of sodium and potassium intake. A longitudinal study

ABSTRACT BACKGROUND: Evaluation of sodium and potassium intake can be carried out using different methods. Biological markers are able to capture intra and inter-individual variability and are used as separate measurements of consumption. The aim of this study was to test the validity of a single measurement of urinary sodium and potassium excretion as representative of habitual intake. DESIGN AND SETTING: Longitudinal study, federal university. METHODS: Food consumption data from a sample of adult university students and public servants (25 to 74 years old) were collected through 24-hour records and 12-hour urinary sodium and potassium excretion at five different times over a one-year period. The dietary data were entered into a nutritional research data software system and the sodium and potassium intakes were estimated. The variables were tested for normal distribution using the Kolmogorov-Smirnov test. One-way analysis of variance or the Kruskal-Wallis test was used to evaluate means. Correlations between measurements using Pearson or Spearman coefficients were calculated. The degree of agreement between the five measurements was given by the intraclass correlation coefficient. RESULTS: Satisfactory agreement was found between the five measurements of urinary sodium and potassium excretion over a year, with little variability in consumption. CONCLUSION: A single measurement of urinary sodium and potassium accurately estimated the usual average consumption of these electrolytes. This can be used in population-based studies.

摘要
研究背景：钠与钾摄入水平可通过多种方法开展评估。生物标志物能够捕捉个体内及个体间的变异特征，可作为摄入水平的独立检测指标。本研究旨在验证单次尿液钠、钾排泄量作为习惯性摄入水平代表指标的有效性。
研究设计与实施场景：纵向研究，实施于联邦公立大学。
研究方法：本研究纳入25至74岁的成年在校大学生及公职人员作为研究对象，通过24小时饮食记录法采集膳食摄入数据，并在为期1年的周期内分5个时间点采集12小时尿液样本以检测钠、钾排泄量。将膳食数据录入营养研究数据管理软件系统，进而估算钠与钾的摄入水平。采用柯尔莫哥洛夫-斯米尔诺夫检验（Kolmogorov-Smirnov test）对各变量进行正态分布检验；采用单因素方差分析或克鲁斯卡尔-沃利斯检验（Kruskal-Wallis test）对均值进行比较分析；采用皮尔逊相关系数（Pearson coefficients）或斯皮尔曼相关系数（Spearman coefficients）计算各检测结果间的相关性；采用组内相关系数（intraclass correlation coefficient）评估5次检测结果的一致性程度。
研究结果：在为期1年的5次尿液钠、钾排泄量检测中，各结果间一致性良好，受试者的摄入水平变异度较低。
研究结论：单次尿液钠、钾排泄量可准确估算受试者日常平均电解质摄入水平，该方法可应用于人群相关研究。