Variations in the Urinary Iodine Concentration and Urinary Iodine/Creatinine Ratio among Preschool Children

An, Dong; Yang, Rui; Du, Yuping; Wang, Xuan; Yang, Ying; Guo, Wenxing; Yang, Junhong; Meng, Dongmei; Gao, Weiwei; Zhang, Jiayi; Chen, Wen; Zhang, Wanqi

doi:https://doi.org/10.1155/2023/6779094

International Journal of Endocrinology

On this page

Abstract Introduction Materials and Methods Results Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 6779094 | https://doi.org/10.1155/2023/6779094

Variations in the Urinary Iodine Concentration and Urinary Iodine/Creatinine Ratio among Preschool Children

Dong An,^1,2Rui Yang,¹Yuping Du,³Xuan Wang,¹Ying Yang,¹Wenxing Guo,¹Junhong Yang,²Dongmei Meng,²Weiwei Gao,²Jiayi Zhang,²Wen Chen,¹and Wanqi Zhang¹

Academic Editor: Liaqat Hussain

Received09 Mar 2023

Revised16 Oct 2023

Accepted25 Oct 2023

Published23 Nov 2023

Abstract

Variations in different urinary measurements for evaluating iodine status are concerning to clinicians and researchers. The present study aimed to analyze the interindividual and intraindividual variations in the urinary iodine concentration (UIC) and urinary iodine/creatinine (UI/Cr) ratio and evaluate their application in assessing the iodine nutrition of preschool children. Four repeated spot urine samples were collected from 163 children at different times within one day. The urinary iodine concentration (UIC) and urinary creatinine concentration (UCr) were measured, and the UI/Cr ratio was calculated. The UIC ( < 0.001) and urinary iodine/creatinine ratio ( = 0.019) of multiple measurements were significantly different. The UIC of morning urine was highest (99.83 μg/L) and then gradually decreased with collection time ( < 0.001). In contrast, the UI/Cr ratio of morning urine samples increased with collection time. By computing the mean intraindividual and interindividual coefficients of variance (CV), the intraindividual variation of the UI/Cr ratio (68%) was significantly lower than that of the UIC (86%). Nevertheless, the interindividual variation was lowest in the UIC (78.62%) of morning urine. In addition, the UIC and UI/Cr ratio showed moderate correlations (r = 0.52, < 0.001), with kappa values of 0.42 in assessing iodine nutrition. The UIC of morning urine samples taken at 8:00–10:00 am was perhaps more stable and reliable in evaluating the iodine nutrition of preschool children at the population level. The UI/Cr ratio showed lower intraindividual variation and may be more suitable for assessing individual iodine nutrition.

1. Introduction

Normal thyroid gland function is critical for early neurocognitive development and growth and development [1]. As a result, more studies have demonstrated the need for early identification and treatment of thyroid disease in children and adolescents during the fetal period [2, 3]. Primary thyrotropin or thyroxine (T4) testing can efficiently screen for congenital hypothyroidism to ensure normal development and cognition [4]. Iodine is an essential component of the hormones produced by the thyroid gland. Therefore, thyroid hormones and iodine are vital for maintaining normal thyroid function [1]. Iodine prophylaxis and periodic monitoring of iodine nutrition in populations are cost-effective approaches to reduce adverse effects of iodine malnutrition across the lifespan [5]. Iodine is primarily obtained through diet and iodized salt and excreted in urine [6]. The 24-h urinary iodine excretion (UIE) is generally considered the most reliable measurement for assessing iodine nutritional status [7, 8]. However, since 24-h urine collection is far inferior to spot urine collection in time, cost, and feasibility, it is challenging to apply it to assess the iodine nutrition of the population. WHO recommends measuring the urinary iodine concentration (UIC) to evaluate population iodine nutrition [9]. The UIC in spot urine samples varies substantially due to variations in daily food and fluid intake [7]. Intraindividual variations in the UIC can considerably affect its reliability in estimating iodine nutritional status [10–12]. It has been estimated that >10 repeated spot urine samples from an individual are needed to reliably assess individual iodine intake [10].

As a more accurate indicator of iodine levels than the UIC, the urinary iodine/creatinine (UI/Cr) ratio is often used [13–15]. Creatinine is a breakdown product of creatine and is steadily excreted through urine if fluid intake is regular [16]. The UI/Cr ratio in single spot urine samples quantifies individual urinary iodine, which has obvious advantages over the 24-h UIE in terms of time and cost [17, 18]. The intraindividual variation of the UIC has been monitored in adults [10], and the UI/Cr ratio in single spot urine samples has been applied to assess iodine nutrition in adults [11, 19–21].

However, little is known about the intraindividual variation in the UIC and the feasibility of the above evaluation methods for preschool children. Evaluating and comparing the reliability of the UIC and UI/Cr ratio in evaluating the iodine nutrition of preschool children could provide data support for clinicians to monitor the iodine nutritional status of preschool children using appropriate biological indicators. This study repeatedly collected spot urine samples from preschool children within one day, analyzed the intraindividual and interindividual variations in the UIC and UI/Cr ratio, and aimed to evaluate the application of the UIC and UI/Cr ratio in assessing the iodine nutrition of preschool children.

2. Materials and Methods

2.1. Study Design and Subjects

This cross-sectional study recruited children aged 3–6 years old who visited Tianjin Children’s Hospital, Tianjin, China, from January to December 2021. All included children were admitted to the respiratory department of the hospital for pneumonia, bronchopneumonia, or bronchiectasis but were able to eat normally. The exclusion criteria were as follows: (1) a history of previous or current thyroid disease, autoimmune disease, endocrine-related disease, heart-related disease, genetic metabolic disease, etc.; (2) the use of iodine-containing drugs such as amiodarone or contrast agents before and during the investigation; and (3) chronic protein-energy malnutrition and particular dietary habits due to disease. Approximately 200 patients who met the eligibility criteria were approached to participate in the study within the proposed time frame, and those who declined did so mainly due to disinterest or being in a hurry. The sample size was estimated based on the number of potential participants who were available for recruitment and who could meet the inclusion criteria within the proposed study time. Written informed consent was obtained from parents or legal guardians, and assent was obtained from the study participants. The Medical Ethics Committee of Tianjin Medical University approved the research protocols.

2.2. Anthropometric Measurements

The height and weight of the subject children were measured using an electronic height and 82-weight meter (TCS-200 SuHeng). Measurements were rounded up to the nearest 0.1 kg for weight and the nearest 0.1 cm for height. Well-trained nurses performed all measurements. Body mass index (BMI) was calculated as body weight (kg)/height (m²).

2.3. Collection and Determination of Urine Samples

Four repeated spot urine samples were collected from 163 children at different periods within one day. The four repeated urine samples were collected at 8:00 am∼10:00 am, 10:00 am∼12:00 pm, 12:00 pm∼3:00 pm, and 3:00 pm∼6:00 pm. All urine samples were stored in a polyethylene bottle and sent to the Tianjin Key Laboratory of Environmental Nutrition and Population for testing within two weeks.

The UIC was analyzed by inductively coupled plasma-mass spectrometry (ICP-MS; iCAP Q, Thermo Fisher Scientific). The UIC measurements’ total inter-assay and intra-assay CV% were 1.4–3.2% and 0.6–1.8%, respectively. The urinary creatinine concentration (UCr) was measured by the national standard spectrophotometric method. Using this method, the CV for the UCr concentration was 0.2–3.2% in the laboratory. The UI/Cr ratio was calculated as follows: the spot urinary iodine concentration divided by the spot urinary creatinine concentration.

2.4. Categorization of Iodine Nutrition

As recommended by WHO [9], we evaluated the iodine status of preschool children using the UIC and UI/Cr ratio in the present study. Children with a UIC ≥300 μg/L were categorized as having excessive iodine nutrition, those with a UIC of 100–300 μg/L were categorized as having adequate iodine nutrition, and those with a UIC ≤100 μg/L were categorized as having insufficient iodine nutrition, as recommended by WHO [9]. There were no criteria for the use of the UI/Cr ratio in defining iodine status. Since the average UCr concentration in children’s spot urine samples is approximately 0.3 g/L [22, 23], a UI/Cr ratio ≤300 μg/g was considered to indicate insufficient iodine nutrition, a UI/Cr ratio of 300–900 μg/g was considered to indicate adequate iodine nutrition, and a UI/Cr ratio ≥900 μg/g was considered to indicate excessive iodine nutrition.

2.5. Statistical Analysis

All data analyses were carried out using SPSS 19.0 (IBM, Armonk, New York, NY, USA), Microsoft Excel (XP 2007, Microsoft, Redmond, WA, USA), and GRAPH PRISM (version 8.0c, GraphPad Software Inc., La Jolla, CA, USA). The Shapiro–Wilk test was used to check the data distribution with a value > 0.1, indicating that the data followed a normal distribution. For normally distributed data, values are presented as the means ± SDs, including age, weight, height, and protein intake. As the UIC, UCr, and UI/Cr ratio of spot urine samples were not normally distributed, the values are expressed as medians (interquartile ranges). The Friedman nonparametric hypothesis test examined the difference in urinary variables among the four time points. The CV% was the square root of the variance divided by the mean as a percentage. We applied the mean CV to evaluate the intraindividual variation of the urinary variables. The mean CV was calculated by equation (1) [24]. Cohen’s weighted kappa analysis assessed the degree of agreement between the two methods (UIC and UI/Cr ratio) to evaluate preschool children with different iodine statuses. A value <0.05 was considered significant at a two-sided level.

3. Results

A total of 163 preschool-aged children participated in this study. The characteristics of the participants are presented in Table 1. The mean age was 4.5 ± 1.0 years old. The mean height was 108.7 ± 9.1 cm, the mean weight was 18.0 ± 4.6 kg, and the mean BMI was 15.0 ± 2.1 kg/m².

3.1. Differences in the UIC and UI/Cr Ratio among the Four Time Points within One Day

A total of 142 valid morning urine samples were collected from 163 children, while four repeated spot urine samples were collected from them within one day. Regarding morning urine, the median UIC was 84.79 μg/L and the median UI/Cr ratio was 287.74 μg/g. The UIC, UCr, and UI/Cr of spot urine at four collection times are shown in Table 2. The UIC ( < 0.001), UCr ( < 0.001), and UI/Cr ( = 0.019) of the four measurements were significantly different. As presented in Figure 1(a), we found that the UIC of morning urine was highest and then decreased with time, while the trend of UI/Cr was the opposite.

(a)

(b)

3.2. Intraindividual and Interindividual Variations in the UIC and UI/Cr Ratio

The interindividual variations in the UIC and UI/Cr ratio for the four time points are shown in Table 3. The mean CVs of the UIC and UI/Cr ratio at different collection time points were 112.13% and 322.80%, respectively, and the interindividual CV of the UI/Cr ratio at each time point was higher than that of the UIC. In addition, the interindividual variation CV of the UIC was lowest in the morning urine samples, at 78.62%. The intraindividual CV of the UIC and UI/Cr ratio within the same day was 86.39% and 68.35%, respectively. As presented in Figure 1(a), the interindividual variations in the UIC and UI/Cr ratio were higher than the intraindividual variations. In addition, compared with the UIC, for the UI/Cr ratio, the intraindividual variation was lower, while the interindividual variation was higher.

3.3. Correlation and Consistency of the UIC and UI/Cr Ratio in Defining Iodine Nutrition

The iodine status of children, defined by the spot UIC and UI/Cr ratio, is shown in Figure 2(a). Based on the spot UIC, 58.82% of the children were classified as iodine insufficient. A total of 38.97% and 2.21% of children were classified as iodine sufficient and iodine excessive, respectively. According to the spot UI/Cr ratio, 50.74% of the children were classified as iodine insufficient. A total of 39.71% and 9.56% of the children were defined as iodine sufficient and iodine excessive, respectively. When the UIC was used as the indicator, more children were classified as insufficient as when the UI/Cr ratio was used, and the number of children who were classed as iodine excessive was smaller. The kappa value was 0.42, demonstrating the consistency between the UIC and UI/Cr ratio of spot urine samples in defining iodine nutrition. As shown in Figure 2(b), the UIC was positively correlated with the UI/Cr ratio (r = 0.52, < 0.001).

(a)

(b)

4. Discussion

As a more accurate indicator of iodine levels than the UIC, the urinary iodine/creatinine (UI/Cr) ratio is often used [13–15]. Creatinine is a breakdown product of creatine and is steadily excreted through urine with regular fluid intake [16], which is usually used as a simple measure to estimate other urinary biological analytes from the respective ratios. Due to significant variations in the UIC, the UI/Cr ratio is also used to evaluate iodine nutrition status [13–15] as a more accurate indicator in some studies. In contrast, few studies have investigated its applicability for preschool children. In our study, we provided a reference dataset comparing the reliability and stability of the UIC and UI/Cr ratio by calculating CVs. We analyzed the interindividual variations in the UIC and UI/Cr ratio at different collection times. We found that the interindividual variations in the UI/Cr ratio were higher than those in the UIC, which means that using the creatinine-corrected UIC to define iodine nutrition does not apply to all individuals and may even be counterproductive. Many previous studies have indicated that UCr can be affected by many factors, such as age, sex, and physical conditions [25, 26]. Based on observations in Chinese school-age children [27], UCr was not stable in repeated spot urine samples and increased with age; preschool children develop relatively rapidly, which may therefore lead to unstable creatinine levels.

We further analyzed the consistency of the UIC and UI/Cr ratio in evaluating the iodine nutrition status of preschool children. Positive correlations between the UIC and UI/Cr ratio were observed. With no criteria for the UI/Cr ratio in defining iodine nutrition, we estimated the reference urinary creatinine concentration for preschool children [22, 23]. We derived criteria for the UI/Cr ratio to evaluate iodine nutritional status. The kappa values (0.42) showed a fair agreement between the two methods in defining iodine nutrition status in preschool children. The criteria of the UI/Cr ratio to evaluate iodine nutrition in the population need to be further studied.

We also found significant variations in the UIC of spot urine samples collected at different times, with the UIC of morning urine samples being the highest and decreasing with time. In addition, the interindividual variation in morning urine (8:00 a.m.–10:00 a.m.) samples was relatively lower than that in casual urine samples collected at other time points. This may be why the UIC of morning urine samples is regarded as the ideal index to assess iodine nutrition, according to WHO [9]. Previous studies on healthy Swiss volunteers aged 4–60 years found that the UIC circadian rhythm of random urine samples increases from noon to midnight; therefore, collecting urine samples between 8:00 a.m. and 11:00 a.m. seems reasonable [28]. Some studies have pointed out that collecting the first void is not recommended due to the difficulty in collection [29]. Instead, fasting urine collection may impact the accuracy of the assessment of iodine nutritional status in morning urine samples [30, 31]. On the other hand, limiting fasting requirements for morning urine samples may impact their comparability with urine samples collected at different times due to their relatively higher concentration. This study did not require morning urine to be fasting void urine.

In addition, we found that the intraindividual variation of the UI/Cr ratio (68%) was lower than that of the UIC (86%). For an individual, many factors contribute to the variation in the UIC, such as sex, age, and sociocultural and dietary influences [32]. A previous study showed that variation in iodine excretion in an individual may follow circadian rhythms [28]. As Figure 1(a) shows, the fluctuations were more pronounced at the four time points of the UIC. Intraindividual variation was higher in the UIC than in the UI/Cr ratio, which means that the UI/Cr ratio may be more stable for individual iodine nutrition evaluation.

In our study, the variations in the UIC and UI/Cr ratio in the population (interindividual) were higher than those in individuals (intraindividual). The same results were reported in a study of twenty-two healthy females performed in Switzerland, which reported that the interindividual CV % for the UIC was higher than the individual variation [10]. In the other study, participants were provided with the same diet for every measurement, which may have reduced the interindividual variation. Therefore, single random urine samples are more suitable for direct application to define iodine nutrition at the population level.

According to Andersen et al., the number of spot urine samples needed to determine the UIC to evaluate iodine nutrition in a population with 95% confidence within a precision range of ±5% is 500 [19]. However, their study focused on Caucasian adult men (CV = 57%), and the CV (78%) of preschool children in our study was relatively high. The estimated sample size with specified precisions was calculated by equation N = (Z × CV %/D)² [19]. The precision range (D) was used to estimate the precision of a set point in biochemical variables and was recommended for estimating the number of samples required for biochemical measurements. The 95% CI (Z) was 1.96 [24]. Based on the equation, the number of spot urine samples needed to determine the UIC to evaluate the iodine nutrition of preschool children with 95% confidence within a precision range of ±5% was 1000. However, a sample size of this magnitude makes estimating (with a 95% CI) the iodine status from spot urine samples within a precision range of ±7% possible.

The present study has several limitations. As the study was conducted in the hospital, the iodine nutrition of participating children may be affected by recent poor dietary intake, resulting in limited generalization of our results. However, the circadian rhythm of the UIC may not be affected since the included children were basically healthy.

Furthermore, although within one day, the intraindividual variation in the UI/Cr ratio was lower than that in the UIC, and exploring the suitability of the UI/Cr ratio for evaluating individual iodine nutrition still requires several days of intraindividual variation. Our study evaluated intraindividual and interindividual variations in the UIC and UI/Cr ratio by collecting repeated spot urine samples from individual children. Few studies have evaluated the reliability and variability of the UIC and UI/Cr ratio in assessing the iodine status of a population or an individual. In this instance, our study provided a reference dataset.

5. Conclusions

Our study shows that the UIC of morning urine at 8:00–10:00 am was perhaps more stable and reliable in evaluating iodine nutrition in preschool children at the population level; the UIC of morning urine samples may be a more reliable and cost-effective indicator for clinicians to assess iodine nutrition in preschool children. The UI/Cr ratio had lower intraindividual variation and may be more promising in evaluating the individual iodine nutrition of preschool children.

Data Availability

The data that support the findings of this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (NSFC Grant No. 82273629) and Tianjin Key Laboratory of Environment, Nutrition and Public Health (2020ENKL01). The authors thank Tianjin Children’s Hospital for its strong support and help in the field investigation.

References

A. J. Forhead and A. L. Fowden, “Thyroid hormones in fetal growth and prepartum maturation,” Journal of Endocrinology, vol. 221, no. 3, pp. 87–103, 2014.
View at: Publisher Site | Google Scholar
P. Hanley, K. Lord, and A. J. Bauer, “Thyroid disorders in children and adolescents: a review,” JAMA Pediatrics, vol. 170, no. 10, pp. 1008–1019, 2016.
View at: Publisher Site | Google Scholar
S. Y. Lee and E. N. Pearce, “Testing, monitoring, and treatment of thyroid dysfunction in pregnancy,” Journal of Clinical Endocrinology and Metabolism, vol. 106, no. 3, pp. 883–892, 2021.
View at: Publisher Site | Google Scholar
J. Léger, A. Olivieri, M. Donaldson et al., “European Society for Paediatric Endocrinology consensus guidelines on screening, diagnosis, and management of congenital hypothyroidism,” Hormone Research in Paediatrícs, vol. 81, no. 2, pp. 80–103, 2014.
View at: Publisher Site | Google Scholar
M. B. Zimmermann, “The role of iodine in human growth and development,” Seminars in Cell and Developmental Biology, vol. 22, no. 6, pp. 645–652, 2011.
View at: Publisher Site | Google Scholar
M. E. Shils and R. K. Rude, “Deliberations and evaluations of the approaches, endpoints and paradigms for magnesium dietary recommendations,” The Journal of Nutrition, vol. 126, no. 9 Suppl, pp. 2398–2403, 1996.
View at: Publisher Site | Google Scholar
T. Remer, N. Fonteyn, U. Alexy, and S. Berkemeyer, “Longitudinal examination of 24-h urinary iodine excretion in schoolchildren as a sensitive, hydration status-independent research tool for studying iodine status,” The American Journal of Clinical Nutrition, vol. 83, no. 3, pp. 639–646, 2006.
View at: Publisher Site | Google Scholar
P. Vejbjerg, N. Knudsen, H. Perrild et al., “Estimation of iodine intake from various urinary iodine measurements in population studies,” Thyroid: Official Journal of the American Thyroid Association, vol. 19, no. 11, pp. 1281–1286, 2009.
View at: Publisher Site | Google Scholar
World Health Organization, Assessment of Iodine Deficiency Disorders and Monitoring Their Elimination: A Guide for Programme Managers, World Health Organization, Geneva, Switzerland, 2007.
F. König, M. Andersson, K. Hotz, I. Aeberli, and M. B. Zimmermann, “Ten repeat collections for urinary iodine from spot samples or 24-hour samples are needed to reliably estimate individual iodine status in women,” The Journal of Nutrition, vol. 141, no. 11, pp. 2049–2054, 2011.
View at: Publisher Site | Google Scholar
L. B. Rasmussen, L. Ovesen, and E. Christiansen, “Day-to-day and within-day variation in urinary iodine excretion,” European Journal of Clinical Nutrition, vol. 53, no. 5, pp. 401–407, 1999.
View at: Publisher Site | Google Scholar
K. E. Charlton, M. J. Batterham, L. M. Buchanan, and D. Mackerras, “Intraindividual variation in urinary iodine concentrations: effect of adjustment on population distribution using two and three repeated spot urine collections,” BMJ Open, vol. 4, no. 1, Article ID e003799, 2014.
View at: Publisher Site | Google Scholar
I. Konrade, L. Neimane, M. Makrecka et al., “A cross-sectional survey of urinary iodine status in Latvia,” Medicina, vol. 50, no. 2, pp. 124–129, 2014.
View at: Publisher Site | Google Scholar
H. K. Kim, S. Y. Lee, J. In Lee et al., “Daily urine iodine excretion while consuming a low-iodine diet in preparation for radioactive iodine therapy in a high iodine intake area,” Clinical Endocrinology, vol. 75, no. 6, pp. 851–856, 2011.
View at: Publisher Site | Google Scholar
Y. Fuse, T. Ohashi, S. Yamaguchi, M. Yamaguchi, Y. Shishiba, and M. Irie, “Iodine status of pregnant and postpartum Japanese women: effect of iodine intake on maternal and neonatal thyroid function in an iodine-sufficient area,” Journal of Clinical Endocrinology and Metabolism, vol. 96, no. 12, pp. 3846–3854, 2011.
View at: Publisher Site | Google Scholar
O. P. Soldin, “Controversies in urinary iodine determinations,” Clinical Biochemistry, vol. 35, no. 8, pp. 575–579, 2002.
View at: Publisher Site | Google Scholar
S. J. Schwab, R. L. Christensen, K. Dougherty, and S. Klahr, “Quantitation of proteinuria by the use of protein-to-creatinine ratios in single urine samples,” Archives of Internal Medicine, vol. 147, no. 5, pp. 943-944, 1987.
View at: Publisher Site | Google Scholar
V. C. Chitalia, J. Kothari, E. J. Wells et al., “Cost-benefit analysis and prediction of 24-hour proteinuria from the spot urine protein-creatinine ratio,” Clinical Nephrology, vol. 55, no. 6, pp. 436–447, 2001.
View at: Google Scholar
S. Andersen, J. Karmisholt, K. M. Pedersen, and P. Laurberg, “Reliability of studies of iodine intake and recommendations for number of samples in groups and in individuals,” British Journal of Nutrition, vol. 99, no. 4, pp. 813–818, 2008.
View at: Publisher Site | Google Scholar
N. Knudsen, E. Christiansen, M. Brandt-Christensen, B. Nygaard, and H. Perrild, “Age- and sex-adjusted iodine/creatinine ratio. A new standard in epidemiological surveys? Evaluation of three different estimates of iodine excretion based on casual urine samples and comparison to 24 h values,” European Journal of Clinical Nutrition, vol. 54, no. 4, pp. 361–363, 2000.
View at: Publisher Site | Google Scholar
L. B. Rasmussen, A. Carlé, T. Jørgensen et al., “Iodine intake before and after mandatory iodization in Denmark: results from the Danish investigation of iodine intake and thyroid diseases (DanThyr) study,” British Journal of Nutrition, vol. 100, no. 1, pp. 166–173, 2008.
View at: Publisher Site | Google Scholar
D. T. Mage, R. H. Allen, and A. Kodali, “Creatinine corrections for estimating children's and adult's pesticide intake doses in equilibrium with urinary pesticide and creatinine concentrations,” Journal of Exposure Science and Environmental Epidemiology, vol. 18, no. 4, pp. 360–368, 2008.
View at: Publisher Site | Google Scholar
H. Kesteloot and J. V. Joossens, “On the determinants of the creatinine clearance: a population study,” Journal of Human Hypertension, vol. 10, no. 4, pp. 245–249, 1996.
View at: Google Scholar
Z. F. Ma, “Intra-individual and inter-individual variations in iodine intake and excretion in adult women: implications for sampling,” British Journal of Nutrition, vol. 123, no. 9, p. 1078, 2020.
View at: Publisher Site | Google Scholar
D. J. Greenblatt, B. J. Ransil, J. S. Harmatz, T. W. Smith, D. W. Duhme, and J. Koch-Weser, “Variability of 24-hour urinary creatinine excretion by normal subjects,” The Journal of Clinical Pharmacology, vol. 16, no. 7, pp. 321–328, 1976.
View at: Publisher Site | Google Scholar
S. S. Waikar, V. S. Sabbisetti, and J. V. Bonventre, “Normalization of urinary biomarkers to creatinine during changes in glomerular filtration rate,” Kidney International, vol. 78, no. 5, pp. 486–494, 2010.
View at: Publisher Site | Google Scholar
W. Chen, X. Li, X. Guo et al., “Urinary iodine excretion (UIE) estimated by iodine/creatinine ratio from spot urine in Chinese school-age children,” Clinical Endocrinology, vol. 86, no. 4, pp. 628–633, 2017.
View at: Publisher Site | Google Scholar
C. Als, A. Helbling, K. Peter, M. Haldimann, B. Zimmerli, and H. Gerber, “Urinary iodine concentration follows a circadian rhythm: a study with 3023 spot urine samples in adults and children,” Journal of Clinical Endocrinology and Metabolism, vol. 85, no. 4, pp. 1367–1369, 2000.
View at: Publisher Site | Google Scholar
Z. Liu, Y. Lin, J. Wu et al., “Is the urinary iodine/creatinine ratio applicable to assess short term individual iodine status in Chinese adults? Comparison of iodine estimates from 24-h urine and timed-spot urine samples in different periods of the day,” Nutrition and Metabolism, vol. 19, no. 1, p. 27, 2022.
View at: Publisher Site | Google Scholar
W. Liu, P. Zhang, X. Zhao et al., “Consistent iodine status assessment in Chinese adults by different spot urinary iodine concentrations in a day together with corresponding correction coefficients,” Journal of the American College of Nutrition, vol. 38, no. 7, pp. 606–613, 2019.
View at: Publisher Site | Google Scholar
N. Konno, K. Yuri, K. Miura, M. Kumagai, and S. Murakami, “Clinical evaluation of the iodide/creatinine ratio of casual urine samples as an index of daily iodide excretion in a population study,” Endocrine Journal, vol. 40, no. 1, pp. 163–169, 1993.
View at: Publisher Site | Google Scholar
C. Als, K. Lauber, L. Brander, D. Lüscher, and H. Rösler, “The instability of dietary iodine supply over time in an affluent society,” Experientia, vol. 51, no. 6, pp. 623–633, 1995.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2023 Dong An et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

116

Downloads

153

Citations