What is the means of assessing iodine in human?

Biochemical assessment of Iodine;

Iodine;

Iodine is a trace mineral utilized by the body to synthesize thyroid hormones triiodothyronine (T3) and thyroxine(T4) . Apart, iodine performs several functions within the body i.e. mobilize stored, iodine yield extra energy and is necessary for proper functioning and development of the brain.

Urinary Iodine Concentration:

Urinary iodine concentration (UIC) is the most common method for assessing iodine nutrition at a population level. UIC reflects recent dietary iodine intake and is thus sensitive to daily fluctuations. It's measured using either colorimetric (Sandell-Kolthoff reaction) or inductively coupled plasma mass spectrometry methods. Despite its variability, UIC is an effective tool for epidemiological surveys.

Serum Thyroglobulin:

Serum thyroglobulin (Tg) has emerged as an additional indicator of iodine status, particularly useful for detecting mild to moderate iodine deficiency. Tg is a sensitive marker of thyroid function and changes in iodine intake. It should be used in conjunction with UIC, particularly in populations at risk of iodine deficiency.

Serum Thyroid Hormones:

Serum thyroid-stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3) concentrations also provide valuable insights into an individual's iodine status. Alterations in these hormones could indicate iodine deficiency or excess. Elevated TSH levels, reduced T4, and increased or decreased T3 may reflect an iodine imbalance.

Iodine Content in Breast Milk

For lactating women, assessing the iodine content in breast milk can provide an indirect measure of the mother's iodine status and the iodine nutrition of the breastfed infant. It's a valuable indicator in perinatal and infant health.

Neonatal TSH Concentration

Neonatal TSH concentration, often measured from dried blood spots as part of newborn screening programs, can indicate iodine deficiency in a population. A high prevalence of elevated TSH levels in newborns may suggest iodine deficiency in the maternal and neonatal population.

Deficiency of iodine;

In many countries, iodine is added in the salt to prevent iodine deficiency disorder (IDD) or goiter. Iodine deficiency lead to several disorder collectively termed as iodine deficiency disorder (IDD). Over last three decades, iodine nutrition has distinctively improved in term of household accessibility to iodized salt.

Low level of iodine may not only disrupt thyroid function but can lead to an abnormal enlargement of thyroid gland, a condition termed as goiter. In children, it can also result mental disabilities, since it is known as the single important preventable cause of brain damage.

Measurement of iodine status;

Four indicator are recommended for the assessment of iodine deficiency in individuals and population group.

a) Urinary iodine concentration(UIC);

Urinary iodine is an excellent biomarker of recent iodine intake and can be analyses(microg/L)in spot urine specimens. Subsequently , daily iodine intake for population estimates can be extrapolated using 24-hour mean urine volume through the following formula, assuming an average bioavailable of iodine as 92% using this expression, a median UIC of 100 microg/L in an adult corresponds roughly to an average daily iodine intake of 150mg.

b) Thyroid size ;

The two methods generally adopted for assessment of iodine status among population are palpation or neck inspection, and thyroid ultrasonography. Through palpation, ''a thyroid is considered goitrous when each lateral lobe has a volume greater than the terminal phalanx of the thumbs of the subject being examined '' .

According to the WHO classification, grade 0 is assigned to a thyroid gland that is not palpable or visible, grade 1 is a goiter that is palpable but not - visible under normal positioning of the neck (i.e. thyroid is not noticeably enlarged), and grade 2 goiter is a thyroid gland that is clearly evident when the neck is in a normal position. Goiter surveys are usually done in school aged children.

It is pertinent to mention that palpation of goiter in the areas of mild iodine deficiency has poor sensitivity and specificity; measurement of thyroid volume (Tvol) by ultrasound is preferable in such situations. thyroid ultrasound s non invasive, quick (2-3 min per subject) and feasible even in remote areas using portable equipment.

Thyroid stimulating hormone(TSH);

Thyroid stimulating hormone circulate in the blood stream and is helpful in determining iodine nutrition. However, it is not a sensitive biomarker of iodine status in elderly.

Conclusion:

Accurate assessment of iodine status involves several biochemical tests, each providing unique insights into iodine nutrition and thyroid function. UIC remains the most used method, although serum markers and other indirect measures are increasingly recognized for their complementary value. Ongoing research continues to enhance our understanding of the complex mechanisms and measures of iodine nutrition.