INNTA (National Institute of Nutrition and Food Technology), SURVEN (Nutrition Surveillance and Epidemiology in Tunisia) Research Laboratory, 11 Rue Jebel Lakhdar, bab Saadoun, 1007, Tunis, Tunisia.
Center of Urgent Medical Assistance of Tunis, Laboratory of Toxicology and Environment (LR12SP07), 10, Rue Abou El Kacem Chabbi, Montfleury, 1008, Tunis, Tunisia.
Biol Trace Elem Res. 2018 Dec;186(2):337-345. doi: 10.1007/s12011-018-1317-y. Epub 2018 Mar 26.
Urinary iodine concentration (UIC) is commonly used to assess iodine status of subjects in epidemiological surveys. As pre-analytical factors are an important source of measurement error and studies about this phase are scarce, our objective was to assess the influence of urine sampling conditions on UIC, i.e., whether the child ate breakfast or not, urine void rank of the day, and time span between last meal and urine collection. A nationwide, two-stage, stratified, cross-sectional study including 1560 children (6-12 years) was performed in 2012. UIC was determined by the Sandell-Kolthoff method. Pre-analytical factors were assessed from children's mothers by using a questionnaire. Association between iodine status and pre-analytical factors were adjusted for one another and socio-economic characteristics by multivariate linear and multinomial regression models (RPR: relative prevalence ratios). Skipping breakfast prior to morning urine sampling decreased UIC by 40 to 50 μg/L and the proportion of UIC < 100 μg/L was higher among children having those skipped breakfast (RPR = 3.2[1.0-10.4]). In unadjusted analyses, UIC was less among children sampled more than 5 h from their last meal. UIC decreased with rank of urine void (e.g., first vs. second, P < 0.001); also, the proportion of UIC < 100 μg/L was greater among 4th rank samples (vs. second RPR = 2.1[1.1-4.0]). Subjects' breakfast status and urine void rank should be accounted for when assessing iodine status. Providing recommendations to standardize pre-analytical factors is a key step toward improving accuracy and comparability of survey results for assessing iodine status from spot urine samples. These recommendations have to be evaluated by future research.
尿碘浓度（UIC）常用于评估流行病学调查中受试者的碘状况。由于分析前因素是测量误差的重要来源，且关于这一阶段的研究较少，因此我们的目的是评估尿样采集条件对 UIC 的影响，即儿童是否吃早餐、当天的尿液排号以及上次进食与尿样采集之间的时间间隔。2012 年进行了一项全国性的两阶段、分层、横断面研究，共纳入 1560 名 6-12 岁儿童。UIC 通过 Sandell-Kolthoff 法测定。通过儿童母亲的问卷调查评估分析前因素。采用多元线性和多项回归模型（RPR：相对流行率比），对碘状况与分析前因素之间的相关性进行了相互调整和社会经济特征调整。与不跳过早餐相比，儿童在早晨采集尿液前跳过早餐会使 UIC 降低 40-50μg/L，且跳过早餐的儿童 UIC<100μg/L 的比例更高（RPR=3.2[1.0-10.4]）。在未调整分析中，UIC 随上次进食后采集尿液的时间间隔延长而降低。UIC 随尿液排号减少而降低（例如，第一次与第二次，P<0.001）；此外，在第 4 次尿液样本中 UIC<100μg/L 的比例更高（与第二次相比，RPR=2.1[1.1-4.0]）。在评估碘状况时，应考虑到儿童的早餐状况和尿液排号。为规范分析前因素提供建议是提高评估点尿样碘状况的调查结果准确性和可比性的关键步骤。这些建议需要通过未来的研究来评估。
