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Urinary iodine concentrations in children, non-pregnant or pregnant women
This indicator assesses urinary iodine concentrations in target groups to determine population impact of salt iodization. This indicator assesses overall population iodine intake. It takes into account other potential dietary sources of iodine, and can detect both deficiency and excess.
Nearly all iodine absorbed from the diet eventually appears in the urine and urinary iodine concentration (UIC) is a well-accepted, cost-efficient and easily obtainable indicator for iodine status. UIC is not only a good marker of recent dietary iodine intake from iodized salt, but also measures intake from all dietary sources. It is also considered a sensitive marker of current iodine intake and can reflect recent changes in iodine status. A profile of iodine concentrations in casual urine specimens provides an adequate assessment of a population’s iodine nutrition. Public health thresholds are established for various population groups defining adequate levels (1, 2).
With rapid global progress in correcting iodine deficiency, examples of iodine excess are being recognized, particularly when salt iodization is excessive and poorly monitored, or when other environmental sources (e.g. drinking water) are rich in iodine. UICs can detect excess iodine intakes in populations.
Population iodine status is presented as the median urinary iodine concentration (the middle value out of all the results) for different populations.
Considerations for the calculations:
a) Use the most recent UIC results collected within the last 5 years.
b) The median urinary iodine concentration should be reported and not the mean. Urinary iodine values tend to not be normally distributed, as a result the median is the preferred measure of central tendency, and percentiles, rather than standard deviations, are most commonly used to describe the distribution of data.
c) Urinary iodine concentrations are not useful for the diagnosis and treatment of individuals but are useful to assess the iodine status of populations. An individual’s urinary iodine concentration can vary daily, or even within the same day, however, these variations tend to even out within populations, providing a useful measure of the iodine status of populations.
d) There are established cut-off points proposed for the median urinary iodine concentration to classify iodine nutrition into different degrees of public health significance for different populations (1). In children and non-pregnant women, median urinary iodine concentrations of between 100 μg/L and 199 μg/L define a population as sufficient. In addition, not more than 20% of samples should be below 50 μg/L (1).
Urinary iodine concentrations, excretion, iodine deficiency, iodine excess,
Food fortification
Outcome
Improved development, Improved intake of vitamins and minerals, Improved nutritional status
All
Early childhood development, Emergency setting or displaced population, Lactation, Pregnancy
Iodine
Market-based
Since casual specimens are collected, it is desirable to measure at least 300 samples from a given population to allow for varying degrees of subject hydration and other biological variations among individuals.
All laboratories analyzing urinary iodine concentrations should have clearly defined internal quality control procedures in place, and should be opened to external audit. In addition, all laboratories should participate in an external quality control program in conjunction with a recognized reference laboratory. This is important because unrecognized iodine contamination has been a common occurrence in urinary iodine concentration laboratories.
Urinary iodine concentration is currently the most practical biochemical marker for iodine nutrition when carried out with appropriate technology and sampling.
Simple modern methods make it feasible to process large numbers of samples at a low cost.
Acceptance by participants to provide a urine sample in survey settings is very high, and casual urine specimens are easy to obtain.
This approach assesses only recent iodine intake.
Urinary iodine assay methods are not difficult to learn or use, but meticulous attention is required to avoid contamination with iodine at all stages.
In a country, the Federal Office for Public Health supports national monitoring of iodine nutrition in schoolchildren (6 to 12 years old) and pregnant women at 5-year intervals. The population-based survey is representative of schoolchildren and pregnant women in the country. Following World Health Organization recommendations for cluster sampling in iodine surveys for the pregnant women and school children, 30 clusters were selected including 20-30 participants. An ethical committee approved the survey, and written informed consent was obtained from all participants and/or their parents. A casual urine sample was collected, transported to a central laboratory, and the iodine concentration measured. The urinary iodine concentration was expressed in micrograms per liter and compared to the World Health Organization reference cut-offs for classification of population iodine nutrition using the median urinary iodine concentration. The results showed that the median urinary iodine concentrations for both schoolchildren (124 µg/L) and pregnant women (187 µg/L) were in the range indicating adequate iodine nutrition.
1. Urinary iodine concentrations for determining iodine status deficiency in populations. Vitamin and Mineral Nutrition Information System. Geneva: World Health Organization; 2013 (http://www.who.int/iris/bitstream/10665/85972/http://apps.who.int//iris/bitstream/10665/85972/1/WHO_NMH_NHD_EPG_13.1_eng.pdf, accessed 28 January 2015).
2. Rohner F, Zimmermann M, Jooste P, Pandav C, Caldwell K, Raghavan R, et al. Biomarkers of nutrition for development--iodine review. J Nutr. 2014;144:1322S-42S. doi:10.3945/jn.113.181974.