| Objectives1. To evaluate the validity of iodine/creatinine adjustments from spot urines in estimating 24 h urinary iodine excretion(UIE) in school-age children.2. To study on the urinary creatinine excretion(UCr E) of school-age children and the main factors that influence the urinary creatinine excretion, aimed to provide theoretical data for the development of urinary creatinine excretion standards in school-age children.Methods A cross-sectional survey in Ningjin and Lingxian Counties of Dezhou City and Dongchangfu District and Gaotang County of Liaocheng City, Shandong Province.Healthy children in grade two to grade six of primary schools were enrolled.Inclusion criteria was as follows: children had no thyroid diseases, other autoimmune diseases, and iodine contained medication. Basic information of name, sex and birth date were recorded. Height and weight were measured, and 3-day dietary questionnaire was writed by every children. Twice repeated 24 h urine and spot urine samples were collected in a three week interval and 24 h urinary volume were measured. Measured 24 h UIE was calculated by 24 h urinary iodine concentration(UIC) multiplying 24 h urinary volume, while estimated 24 h UIE was calculated by spot urinary iodine/creatinine ratio(UI/Cr) multiplying 24 h UCrE.Results1. In the first collection, the estimated 24 h UIE was significantly lower than measured24 h UIE(Z=-17.198, P<0.001). But in the second collection, no difference was observed in measured 24 h UIE and estimated 24 h UIE(Z=-0.669, P=0.503).2. In twice repeated urinary collections, spot UIC(r=0.591, P<0.001; r=0.625,P<0.001), spot UI/Cr(r=0.636, P<0.001; r=0.727, P<0.001), 24 h UIC(r=0.678,P<0.001; r=0.764,P<0.001) and estimated 24 h UIE(r=0.849, P<0.001; r=0.901,P<0.001) were strongly correlated with measured 24 h UIE respectively. The estimated 24 h UIE has the highest correlation coefficient in all urinary iodine indexes.3. In Bland-Altman plots analysis, the mean ratio of estimated 24 h UIE versus measured 24 UIE was 0.81(95% CI: 0.32-2.06) in the first collection. While in the second collection, the mean ratio of estimated 24 h UIE versus measured 24 h UIE was0.96(95%CI: 0.39-2.36).4. Describing the iodine nutritional distribution of school-age children by use of measured 24 h UIE and estimated 24 h UIE. The Kappa value of consistency analysis was 0.6(P<0.001) in the first collection, and the Kappa value was 0.7(P<0.001) in the second collection.5. In protein sufficient children, age(r=0.365, P<0.001), height(r=0.418, P<0.001),weight(r=0.480, P<0.001), BSA(r=0.486, P<0.001) and BMI(r=0.391, P<0.001)were strong correlated with 24 h UCr E respectively. While the protein intake(r=0.058,P<0.001) was in a very weak correlation with 24 h UCr E. In protein insufficient children, age(r=0.275, P<0.001), height(r=0.360, P<0.001), weight(r=0.414,P<0.001), BSA(r=0.414, P<0.001), BMI(r=0.341, P<0.001) and protein intake(r=0.205, P<0.001) were strong correlated with 24 h UCr E respectively.6. In protein sufficient children, estimated 24 h UIE was calculated by spot UI/Cr multiplying 24 h UCr E reference by BSA groups. In twice repeated urinary collections,spot UIC(r=0.464, P<0.001; r=0.464, P<0.001), spot UI/Cr(r=0.565, P<0.001;r=0.636, P<0.001) and estimated 24 h UIE(r=0.604, P<0.001; r=0.636, P<0.001)were strongly correlated with measured 24 h UIE respectively. The estimated 24 h UIE had the highest correlation coefficient. In Bland-Altman plots analysis, the mean ratio of estimated 24 h UIE versus measured 24 UIE was 1.06(95% CI: 0.29-3.78) in the first collection. While in the second collection, the mean ratio of estimated 24 h UIE versus measured 24 h UIE was 0.99(95%CI: 0.27-3.60).Conclusions1. The estimated 24 h UIE was better than spot UI/Cr that may overestimate iodine status of school-age children, and can be used as an effective and reliable indicator to evaluate the iodine status of individuals or population in school-age children.2. The factors affecting urinary creatinine excretion in descending order was BSA,weight, height, BMI and age. Protein intake was strong correlated with 24 h UCr E in protein insufficient children, but was weak in protein sufficient children. It is necessary to take into account these factors to establish school-age children urinary creatinine excretion standard in our country. |
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