**Abstract**

Many reports or manuals had focused on the implementation of iodine deficiency disorder (IDD) elimination programme from the point of view of the programme managers. In this chapter, we will focus on the importance of urinary iodine testing, its related diagnosis and further biomarker testing suggested for further diagnosis related to thyroid health. This chapter will be relevant for the respondents to the monitoring programme, particularly the 8–10-year-old schoolchildren and pregnant women, i.e., the vulnerable targeted groups from either the iodine-deficient areas or the Universal Salt Iodization (USI) gazetted areas. USI has been proposed by the World Health Organization (WHO) as the most cost-effective programme to eliminate IDD, and it is also a way to increase the intelligent quotient (IQ ) of the world population for the future. This chapter had been laid out so that the readers will know briefly the rationale behind the testing of urinary iodine among schoolchildren and pregnant women under the implementation of the USI programmes in their countries and their benefits, especially the utilisation of urinary iodine as the biomarker to portray the population iodine status. Diagnosis including iodine-induced thyroid diseases and further biomarkers measurement besides urinary iodine is also discussed briefly.

**Keywords:** urinary iodine, biomarker, iodine nutrition, population, thyroid status

### **1. Introduction**

#### **1.1 Importance of urinary iodine testing to determine population iodine nutrition**

All iodine in the blood is in the iodide form either it is taken up by the thyroid and converted into thyroid hormone or being excreted in the urine. Almost 90% of the ingested iodine is excreted in the urine. Therefore, urinary iodine excretion is a good biomarker of very recent dietary iodine intake [1]. On an individual basis, 24-hour urine sample is necessary for the assessment of iodine intake as the level is more consistent in iodine-deficient populations than in those with adequate iodine intake (**Figure 1**). On a population basis, the median urinary iodine concentration (mUIC) of spot urine from sufficiently large randomly selected 8–10-year-old children or adults has been shown to provide useful information on the average iodine intake or status of a community. On an individual basis, urinary iodine varies from day to day and even within a given day. However, this variation tends to even out among population [2]. Most of the epidemiological IDD studies had emphasised on rapid inexpensive methods of urinary iodine determination that could be applied to a large number of samples [3].

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*Biochemical Testing - Clinical correlation and Diagnosis*

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[3] Jenkins MA. Serum Protein

Biotechnology; 2000. pp. 11-19

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2009. p. 161

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Benore M. Fundamental Laboratory Approaches for Biochemistry and Biotechnology. Hoboken, NJ: Wiley;

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[6] Tate J, Caldwell G, Daly J, Gillis D, Jenkins M, et al. Recommendations for standardized reporting of protein electrophoresis in Australia and New Zealand. Annals of Clinical Biochemistry. 2012;**49**:242-256

#### **Figure 1.**

*Degrees of iodine intake (iodine nutrition status) and their suitable types of human sample collection to determine the median urinary iodine concentration (mUIC).*

The main biochemical indicator that is widely used for the assessment of IDD is urinary iodine concentration (mUIC) [4]. The advantages of mUIC as an indicator of IDD are that the method directly reflects iodine supply of the individual, it is objective and non-invasive and urine samples can be kept for later analysis. However, the disadvantages of this method are that it requires laboratory space, special facilities and skilled technician to provide accurate determinations. In addition, this method reflects only current but not past intake of iodine [5].

Epidemiological studies stated that the population distribution of urinary iodine is required rather than individual levels. The frequency distribution of urinary iodine usually skewed towards elevated values; hence, the median value is considered instead of the mean as indicating the status of iodine nutrition [1]. The mUIC of 100 μg/L and above defines a population which has no IDD; i.e. at least 50% of the sample should be >100 ug/L. In addition, not more than 20% of sample should be below 50 μg/L. Iodine nutrition status is based on six categories of urinary excretion classification (**Table 1**) [3].


#### **Table 1.**

*Epidemiological criteria for assessing IDD in a population based on median urinary iodine concentration.*

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**Figure 2.**

*Journal of Thyroid Research) [13].*

*Urinary Iodine: Biomarker for Population Iodine Nutrition*

**1.2 Iodine role in thyroid hormone synthesis and its contribution to human body**

Iodine is grouped under micronutrients, and it is needed in small amount, but it is very important for the development of optimum human growth. Iodine is needed in the synthesis of thyroid hormones [6]. Through iodination, one, two, three or four iodine atoms are bound to tyrosine to form monoiodothyronine (MIT), diiodothyronine (DIT), triiodothyronine (T3) or thyroxine (T4), respectively, through the action of iodinase enzyme. Iodine is absorbed from the gastrointestinal system, will enter the blood circulation and will be transported into the thyroid follicle cells through the sodium/iodine (Na/I) symporter. In iodide form, it will then be transported to the thyroid follicle colloid through pendrin. Concurrently, thyroglobulin (TG) is being synthesised in the endoplasmic reticulum (ER) and being secreted into the follicle colloid through exocytosis. TG is the transporter protein of the thyroid hormones in the thyroid follicle colloid. It consists of branches of tyrosine molecules which will then be bound to iodine through the iodination process, forming the MIT and the DIT. When one MIT and one DIT bind, T3 will be formed, while upon binding of two DITs, T4 will then be formed. These TG-bound thyroid hormones will enter the thyroid follicular cell through endocytosis. TG will then undergo proteolysis, and T3 and T4 will be transported into the blood circulation through

Iodine is a micronutrient which is present in the body in minute amount. The

quantity of iodine required by an individual is about 150–200 μg/day [8]. Its main role is in the synthesis of thyroid hormone which is essential for the brain

*Thyroid hormone synthesis in the thyroid gland (image reproduced with permission from the rights holder,* 

*DOI: http://dx.doi.org/10.5772/intechopen.84969*

*1.2.1 Thyroid hormone synthesis*

the MCT symporter [7] (**Figure 2**).

*1.2.2 Iodine's contribution to human body*
