Iodine status assessment

Previous studies (as mentioned above) demonstrated an improvement in the general iodine supply in different areas and different age groups. The underlying reasons for this improvement (e.g., altered nutrition, use of iodinated salt) and its consequences for thyroid pathologies are not always obvious. To clearly assess a populations iodine status, the WHO recommended monitoring the iodine content in salt at the production level, measurement of urinary iodine concentration and carrying out surveys in large cohorts under local circumstances as the most suitable method for iodine status assessment (WHO, 2001). 

Iodine status assessments should also be based on food production surveillance and prospective clinical studies measuring Ul, iodine content in daily diets and goiter prevalence. 

Deficiency of iodine, a component of thyroid hormones, may result in goiter formation (see Chap. 73). However, not everyone with an iodine-deficient diet will develop a goiter. Thyroxine (T4) and triiodothyronine (T3) can be used to assess iodine status (see Table 135-8). Intravenous iodine supplements typically are not necessary except during long-term parenteral nutrition with minimal enteral intake. Iodine needs generally are met by cutaneous absorption of iodine from germicides (e.g., povidone-iodine) used in catheter care or consumption of iodized salt. " Use of povidone-iodine wiU likely decrease with the increased use of chlorhexidine for catheter care, and the need for iodine supplementation must be individualized. Iodine excess is rarely a clinical concern when thyroid function is normal. 

Carle IV, Azuoias JK and Nugent GF (1985) Assessment of iodine status and thyroid function of sheep and goats kept under pastoral conditions. In Mills CF, Brenner I, Chestere JK eds. Trace Fle-ments in Man and Animals - TEMA 5. Famham Royal, Slough SL2 3BN, UK. 

Several indicators are used to assess the iodine status of a population thyroid si2e, UI and the blood constituents, TSH, orTg. 

Because of the variability of iodine content in specialized enteral preparations, the iodine status of individuals should be monitored with prolonged use of these products and regular assessment of goiter, urinary iodine content, and thyroid function tested. Such monitoring is also appropriate if specialized enteral preparations are only part of the total nutritional intake, particularly if protein- and iodine-rich foods are restricted. 

Urinary iodine was, especially, a suitable method to assess iodine status in a large cohort. Urinary iodine... 

The assessment of population, as well as individual iodine status, is most often based on three different proce-dures/indicators (Andersson et ai, 2005 WHO, 2001) ... 

To assess a local populations iodine status, according to the WHO requirements, by measurement of Ul and estimation of nutritional iodine intake and TGP, we used a comprehensive scheme to evaluate iodine status (Brauer et al., 2005) in Leipzig, a previously iodine-deficient area (Gruning et al., 2001 Hampel et al., 1995). We combined the investigation of different sources of iodine and different... 

Results of a Comprehensive Prospective Assessment of Iodine Status in Leipzig... 

Urinary iodine is a suitable method to assess the iodine status in a large cohort. Ul is specific and sensitive, and has the advantage to be more accurate than intake estimations derived from dietary surveys (Knudsen et al., 2002 Brauer et al., 2005 Laurberg et al., 2006 Ovesen and Boeing, 2002). 

Assessment of Iodine Intake and Iodine Status in Vegans... 

The validity of the duplicate portion technique may be problematic as the completeness of duplicate portions is often difficult to assess. However, the use of biochemical markers, such as plasma, serum and urine, may be incorporated into nutritional assessment studies to validate dietary surveys or confirm nutritional status. There are a number of different methods that can be used to assess iodine status and, in particular, for the determination of the severity of iodine deficiency. However, two main methods used for the assessment of iodine status are measurement of urinary iodine excretion and thyroid function tests (an indirect method of iodine sufficiency). 

Five studies have used biochemical markers to assess the iodine status of the vegan population (Tables 45.4 and 45.5). Three studies included measurements of thyroid function, while three measured the urinary iodine excretion of vegan subjects. 

Until the 1990s, total goiter prevalence (TGP) in school-age children was the primary indicator for the assessment of functional consequences of iodine deficiency in the population (WHO et al., 2001). Thyroid size was traditionally determined by palpation, but the reliability of this method is limited by high inter-observer and intra-observer variations. The measurement of thyroid size by ultrasound has therefore been an important step in the detection of mild-to-moderate iodine deficiency. International reference values for normal thyroid size are now available from iodine-sufficient children (Zimmermann et al., 2004). Because TGP is not a sensitive indicator of recent changes in iodine status in the... 

The observations relating to iodine deficiency in pregnancy are firstly those concerned with maternal thyroid function and maternal goiter. Maternal urinary iodine (UI) excretion is the usual method of assessing iodine status in the population at risk or the individual, and is discussed below. Neonatal indicators of maternal iodine deficiency are goiter and neurointellectual impairment. 

Iodine sufficiency in pregnant women is established as a median of urine iodine concentration (UIC) in the population with a value of >200 xg/l, substantially higher than the >100 ig/l recommended in non-pregnant women (Table 73.2). In this sense, a recent report by Travers et ai (2006) showed that the UIC of the population does not reflect other indicators of iodine status, such as neonatal TSH values. This raises the question of what is the most appropriate indicator for assessing iodine status in the general or pregnant population. 

In general, it is assumed that about 90% of ingested iodine is excreted in the urine, and that an equilibrium is established between dietary iodine intake and urinary iodide (UI) excretion. The measurement of UI excretion can therefore provide an accurate approximation of the very recent dietary intake of iodine (UNICEF, 1998) and, therefore, is the index of choice for evaluating the degree of iodine deficiency and its correction (Hetzel and Dunn, 1989). Since the results obtained reflect recent dietary iodine intake, the determination of UI provides little useful information on the long-term iodine status of an individual. Due to thyroidal economy considerations, a relatively high UI measurement usually reflects recent exposure. Iodine concentrations in casual urine (spot) specimens of children or adults provide an adequate assessment... 

Figure 120.5 Iodine status in schoolchildren living in urban and rural areas in Bulgaria assessed on the basis of ioduria. White bars - boys, black bars - girls plain bars - urban area, dotted bars - rural area.

Population Surveys to Assess Iodine Status in Tasmania (1998-2007)... 

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