**4. IDD elimination programme worldwide and Universal Salt Iodization (USI) programme**

Universal Salt Iodization (USI) is currently the most widely used strategy towards sustainable control and elimination of IDD. There was a significant progress since the adoption of USI as a primary strategy to address IDD in 1993. Iodizing table salt is one of the best and least expensive methods of preventing IDD. Salt is used as a key vehicle as it is widely available and consumed in a regular amount throughout the year apart from a very low cost of salt iodization with US\$ 0.05 per person per year [1]. This strategy has been implemented in most countries where iodine deficiency is a public health problem.

Various concerted global efforts have also been undertaken to eliminate IDD. This includes extensive advocacy from the international partners/alliances such as the WHO, UNICEF and ICCIDD (International Council for Control of Iodine Deficiency Disorders). These alliances have been in the forefront in helping countries to set up national salt iodization programmes. As reported by WHO/UNCEF/ ICCIDD, there are currently 65 countries worldwide implementing USI as an effective strategy to eliminate IDD [3]. However, an effective USI in correcting iodine deficiency adequately through iodized salt must reach the whole affected population including pregnant women and children. Therefore, close and regular monitoring of iodized salt at various levels from the production, importation, retailer and household is crucial. Such monitoring requires close collaboration between the governments, salt industries and importers. In countries or areas within countries where USI is not possible, iodine supplementation needs to be implemented and especially targeted to pregnant women and children until USI is scaled up.

#### **5. Urinary iodine results and their implications**

Upon consumption, the needed amount of iodine is retained in the body, while excess iodine is excreted. Thus, high urinary iodine concentration does not reflect a disease state yet, but if persists on repeated urine sample, further blood tests is recommended. Urinary iodine reflects the food consumption taken overnight, and it is just an immediate biomarker (short-term reflection) for iodine intake. Thus, the long-term reflection of iodine intake will be more representative by measuring blood thyroglobulin (TG) as it is synthesised parallel to the amount of iodine present in the thyroid follicular cells. The very low or high individual urinary iodine readings will usually be repeated for testing to ensure that it is replicating the first reading.

### **6. Other blood biomarker measurement to support iodine-deficient status determined through urinary iodine measurement**

For respondents with high mUIC, other biomarkers such as blood thyroglobulin (TG), thyroid-stimulating hormone (TSH), thyroid hormones (free thyroxine, fT4;

**19**

*Urinary Iodine: Biomarker for Population Iodine Nutrition*

**Maximum**

free triiodothyronine, fT3) and thyroid antibodies, thyroid peroxidase antibodies (TPO Ab) and thyroglobulin antibodies (TgAb) are thus suggested for further

*Reference intervals for thyroid hormones from subjects with normal thyroid gland assessed sonographically* 

**Whole group (n = 870) Constraint group (n = 453)**

**Median Minimum-**

**Maximum**

**2.5th–97.5th percentiles**<sup>a</sup>

**2.5th–97.5th percentiles**<sup>a</sup>

TSH, mIU/L 1.31 0.05–14.50 0.30–3.63 1.36 0.12–5.29 0.40–3.77<sup>b</sup> T4, nmol/L 101.00 52.10–209.00 71.50–158.00 98.30 61.80–173.00 70.50–157.00 T3, nmol/L 1.77 0.89–4.00 1.23–2.80 1.77 0.89–3.96 1.27–2.79 FT4, pmol/L 16.20 8.24–28.60 12.70–20.80 16.20 9.30–24.70 12.80–20.40 FT3, pmol/L 5.10 2.52–9.96 3.89–6.66 5.13 2.52–9.96 4.02–6.79

*The lower limit of the TSH reference interval in the constraint group was >5% different from the comparable limit* 

T4 is a molecule of thyronine bond to four atoms of iodine, while T3 has three iodine atoms. T4 is more abundant than T3, but through deiodinase activity, the more potent T3 is synthesised. Low level of T4 usually indicates hypothyroidism. For clinical biochemistry free T4 (fT4) and free T3 (fT3) are usually measured as these are the biologically active forms. Reference intervals for fT4 and fT3 are as stated in **Table 2**.

TSH is released upon the induction by thyrotropin-releasing hormone (TRH), secreted from the hypothalamus. TRH is secreted when serum T3 and/or T4 is low. TSH induces the production of thyroid hormones T3 and T4. Low level of TSH usually indicates hyperthyroidism (parallel to high levels of T3 and/or T4) [17].

TG is the globulin where binding of iodine to tyrosine to form thyroid hormones

takes place. It is the long-term biomarker for iodine status in a human, besides

**6.4 Thyroid antibodies [thyroid peroxidase antibodies (TPO Ab) and** 

The median for reference interval for dried blood spot (DBS) TG from 5- to 14-year-old children before intervention of iodized salt is 49 g/L. After using iodized salt for 5 months, the DBS-TG decreased to 13 g/L and further decreases to

This antibody is for binding to the antigen thyroid peroxidase (TPO) enzyme which is responsible for thyroid hormones synthesis. Once the enzyme is bound to the antibody, less free unbound enzymes are available for thyroid hormone

urinary iodine as the short-term biomarker for iodine nutrition.

8 g/L after 10 months of consumption of iodized salt [20].

**thyroglobulin antibodies (TgAb)]**

diagnosis. Brief information on these biomarkers is as stated below:

**6.1 Free thyroxine (fT4) and free triiodothyronine (fT3)**

*(table reproduced with permission of the rights holder, Clinical Chemistry) [19].*

**6.2 Thyroid-stimulating hormone (TSH)**

Reference interval for TSH is as stated in **Table 2**.

**6.3 Thyroglobulin (TG)**

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

**Hormone Median Minimum-**

*Data are reported as empirical percentiles.*

*a*

*b*

**Table 2.**

*of the whole group.*


*a Data are reported as empirical percentiles.*

*b The lower limit of the TSH reference interval in the constraint group was >5% different from the comparable limit of the whole group.*

#### **Table 2.**

*Biochemical Testing - Clinical correlation and Diagnosis*

iodine deficiency is a public health problem.

difficult to be assessed.

**(USI) programme**

of 150–249 μg/L has been established to determine the adequate iodine status among

from either spot or 24-hour urine samples means that UIC cannot be used to assess iodine status in an individual pregnant woman. Therefore, the association between iodine status in pregnancy and the developmental outcome of the individual child is rather

**4. IDD elimination programme worldwide and Universal Salt Iodization** 

Various concerted global efforts have also been undertaken to eliminate IDD. This

Upon consumption, the needed amount of iodine is retained in the body, while excess iodine is excreted. Thus, high urinary iodine concentration does not reflect a disease state yet, but if persists on repeated urine sample, further blood tests is recommended. Urinary iodine reflects the food consumption taken overnight, and it is just an immediate biomarker (short-term reflection) for iodine intake. Thus, the long-term reflection of iodine intake will be more representative by measuring blood thyroglobulin (TG) as it is synthesised parallel to the amount of iodine present in the thyroid follicular cells. The very low or high individual urinary iodine readings will usually be repeated for testing to ensure that it is replicating the first reading.

**6. Other blood biomarker measurement to support iodine-deficient** 

For respondents with high mUIC, other biomarkers such as blood thyroglobulin (TG), thyroid-stimulating hormone (TSH), thyroid hormones (free thyroxine, fT4;

**status determined through urinary iodine measurement**

includes extensive advocacy from the international partners/alliances such as the WHO, UNICEF and ICCIDD (International Council for Control of Iodine Deficiency Disorders). These alliances have been in the forefront in helping countries to set up national salt iodization programmes. As reported by WHO/UNCEF/ ICCIDD, there are currently 65 countries worldwide implementing USI as an effective strategy to eliminate IDD [3]. However, an effective USI in correcting iodine deficiency adequately through iodized salt must reach the whole affected population including pregnant women and children. Therefore, close and regular monitoring of iodized salt at various levels from the production, importation, retailer and household is crucial. Such monitoring requires close collaboration between the governments, salt industries and importers. In countries or areas within countries where USI is not possible, iodine supplementation needs to be implemented and especially

targeted to pregnant women and children until USI is scaled up.

**5. Urinary iodine results and their implications**

Universal Salt Iodization (USI) is currently the most widely used strategy towards sustainable control and elimination of IDD. There was a significant progress since the adoption of USI as a primary strategy to address IDD in 1993. Iodizing table salt is one of the best and least expensive methods of preventing IDD. Salt is used as a key vehicle as it is widely available and consumed in a regular amount throughout the year apart from a very low cost of salt iodization with US\$ 0.05 per person per year [1]. This strategy has been implemented in most countries where

pregnant women. However, the large intra-individual variation in UIC

**18**

*Reference intervals for thyroid hormones from subjects with normal thyroid gland assessed sonographically (table reproduced with permission of the rights holder, Clinical Chemistry) [19].*

free triiodothyronine, fT3) and thyroid antibodies, thyroid peroxidase antibodies (TPO Ab) and thyroglobulin antibodies (TgAb) are thus suggested for further diagnosis. Brief information on these biomarkers is as stated below:
