Urinary iodine excretion measurement

The urinary iodine excretion measurements in Zagreb and Rude showed mostly borderline values. Although along the coast over 200 ]4g I/g creatinine was found (13), the values in Zagreb and Rude are less than current World Health Organizations recommendation for optimum iodine intake of 150-300 /[Pg.411]

Countries affected by iodine deficiency require to develop national programmes to assess the extent and severity of the problem. Once an IDD control programme is initiated monitoring and evaluation are required. There are three major components needed to meet this goal, namely determination of thyroid size and goitre prevalence, the determination of urinary iodine excretion, and the measurement of thyroid function, including serum TSH levels. 

Urinary Iodine Excretion (UIE) provides the best single measurement of iodine intake of the population and Should be used for initial and follow up assessment. For epidemiological studies, population and not individual levels are is required. To achieve this 40 casual samples from a particular group can be collected (may be collected from schoolchildren at the same time as the goiter is assessed). The values are expressed as a median. Median UIE in the population below 100 pg/1 indicate iodine deficiency. Thus median UIE 10 pg/1 means no deficiency, 50-99 pg/1 indicates mild, 20 9 pg/1 moderate, and <20 pg/1 severe IDD. 

This chapter aims to provide a description of these variations in urinary iodine excretion, some components and determinants of this variation, and the importance of variation for the interpretation of measurements of iodine excretion used to describe iodine nutrition in groups and in individuals. 

Table 44.2 shows measures of dispersion of urinary iodine concentration, and includes estimated 24 h urinary iodine excretion both for individual samples and for the average of 12 monthly samples. 

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). 

As over 90% of the body s iodine is excreted in urine, urinary excretion of iodine is currently the most commonly-used biochemical marker of iodine intake. The determination of urinary iodine excretion in 24-h urine specimens is considered to be the most reliable method (Dunn, 1993) for testing urinary iodine levels. However, the accuracy and validity of the results will depend on the completeness of the 24-h collections hence, measures to assess the completeness of such collections, e.g., urinary creatinine excretion or para-aminobenzoic acid (Gibson, 2005), should be considered. 

The determination of the levels of thyroxine (T4) and TSH in serum may be used to indicate thyroid function, thus providing an indirect measurement of iodine sufficiency. However, although serum T4 and TSH levels can be accurately and precisely measured, the tests tend to be costly and technically time-consuming. In comparison, measurements of urinary iodine excretion are cheaper and technically simpler, with no requirement to take a blood sample. 

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. 

The iodine intake of vegans participating in the Rauma investigation was extremely low, despite the consumption of seaweed, although the levels of serum T4 and TSH were within the normal range (Table 45.4), indicating normal thyroid function, and the urinary iodine excretion level was high (Table 45.5). The difference in dietary iodine intake and biochemical measurements was attributed to the use of seaweed and seaweed products with unknown iodine content. 

These studies highlight that the measurement of urinary iodine excretion may be used as an indicator of iodine intake and deficiency. The specific aim of the research, i.e., estimation of iodine intake in an individual or a population, will influence the sampling method to be used. Quantitative estimates of iodine intake from casual urinary samples are sufficient to give an estimate of intake in a population however, if the aim is to obtain an accurate estimation of habitual iodine intake in an individual,... 

The measurement of urinary iodine excretion may be used as an indicator of iodine intake and deficiency. 

In populations with even mild iodine deficiency, an increased goiter rate can be seen. Delange et al. (1997) have measured thyroid volume and urinary iodine excretion in 5709 children aged 7—15 years in different sites in 12 European countries. All ultrasound examinations and urinary iodine assays were performed by the same investigators. An inverse relationship was found (Figure 55.3). 

Iodine intake can be measured as urinary iodine excretion in a casual urine sample or, preferably, in a 24-h urinary sample. Iodine excretion in a casual urine sample can be expressed as a concentration, as p,g I/g Cr, or as estimated 24-h urinary iodine (p,g/day) if p,g I/g Cr is multiplied by daily expected Cr excretion for the actual age and gender group. However, none of these measures can be used to determine an individual s habitual iodine intake. Iodine intake can also be assessed using dietary intake methods, but like urinary measurements, to determine the habitual iodine intake in an individual, 24-h recalls should be repeated several times or dietary records should be kept for several days (the number of days needed to determine the habitual iodine intake is not known, but is probably more... 

The inverse relationship between low iodine intake and enlarged thyroid size, which obviously must be there, is found when urinary iodine excretion and thyroid enlargement are compared between different populations. Within a population, the relationship can only be expected if a measure for an individual s habitual iodine intake is used and the relationship is corrected for other factors that influence thyroid size in the population. 

The ICCIDD has collaborated closely with the WHO and UNICEF in short-term training programs for country program managers in technical procedures, such as the measurement of thyroid size by ultrasonography and laboratory methods for the measurement of urinary iodine excretion and blood thyroid-stimulating hormone (TSH). 

The introduction of salt iodization in an IDA leads to an improvement in iodine supply, measurable in an increase of urinary iodine excretion. 

In iodine-deficient regions, free tetraiodothyronine (fT4) increases, especially in multinodular goiters, whereas thyroid-stimulating hormone (TSH) levels decrease significantly, especially in multinodular and diffuse goiters (Fassbender et al., 2001). The more contrast agent was used, the more urinary iodine excretion was measured. These observations are probably due to the fact that the thyroid transport mechanism for iodine is not saturated by high-iodine plasma concentrations (Fassbender et al., 2001). The concentration of total T3 remains constant (Fassbender et al., 2001). However, TSH levels decrease in... 

Notes-. Iodine intake expressed as iodine dietary intake and urinary iodine excretion in casuai urine sampies expressed in two ways in maies (M) and femaies (F). Among eideriy subjects in the Nordic countries, the iodine intake seems to be adequate, while the intake has improved in The Netheriands, Great Britain and Germany, in the iatter, though, the assessed iodine intake is still found to be inadequate. The mild iodine deficiency in Switzerland is measured before a scheduled increase in the iodine salt content. N, numbers 3-D R, 3-days food record FFQ, food frequency questionnaire. 

Figure 119.3 Geographical variations in urinary iodine excretion in Denmark before iodine fortification of salt. Median urinary iodine excretion among inhabitants of various Danish cities before iodine fortification of salt, and the estimated number of people living in areas with different levels of urinary iodine excretion. Values were compiled from different studies of urinary iodine excretion, or estimated from measurements of groundwater iodine content. Geographical variation in iodine intake in Denmark is mostly determined by differences in groundwater iodine content. Pedersen etal., (1999) Rasmussen etal., (2000).

Low urinary iodine excretion is being reflected in clinical measures of changes in thyroid hormone levels and increased thyroid volumes. 

Dr. Braverman told us that iodine-induced thyrotoxicosis could be diagnosed by measuring urinary iodine excretion levels. I would like to comment on this point. If the iodine contamination is of recent onset, urinary iodine will of course be elevated. However, several studies have indicated that after coronary arteriography for instance, iodine in urine will be elevated up to two weeks later. After that period it will rapidly come down to normal excretion levels. My other comment concerns the lowering of thjn-oidal radioactive iodine uptake in patients contaminated with iodine. In some patients with iodine-induced thyrotoxicosis, the radioactive iodine uptake remains elevated. Therefore, a high uptake does not exclude the diagnosis of iodine-induced thyrotoxicosis. 

Y.Yabu, K.Miyai, Y.Endo et.al, Urinary iodide excretion measured with an iodine-sensitive ion electrode studies on normal subjects of varying ages and patients with thyroid diseases, Endocrinol Japon 35 391(1988)... 

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