Pre-analytical Factors Influence Accuracy of Urine Spot Iodine Assessment in Epidemiological Surveys

摘要

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 (6-12years) 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 50g/L and the proportion of UIC100g/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 5h from their last meal. UIC decreased with rank of urine void (e.g., first vs. second, P0.001); also, the proportion of UIC100g/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.