Iodine is a micronutrient whose function in the human body is to make Thyroid hormones ,it is absorbed from Gut as iodide in the bloodstream through NIS symporter. There are many inhibitors in the diet which may prevent its uptake through NIS,due to which deficiency of iodine may occur in the body which leads to different thyroid disorders, In the bloodstream iodide is transported to Thyroid Gland where it is again taken by NIS symporter , after NIS takes iodine in the thyroid follicular cells, accumulation of Iodine takes place in the thyroid gland.The thyroid follicular cells secreate a Protein called Thyroglobulin in the Colloid many Thyroglobulin proteins are getting there then iodine atoms start a reaction with the Thyroglobulin proteins amino acid Tyrosine this reaction is called iodination coupling reaction , In this reaction Some tyrosine amino acids take one iodine atom in its ring some take 2 atoms in the ring which we called mono iodination and Di iodination reactions and the resulting molecules are called Monoiodothyronine ,diiodothyronine ..then after this there occurs coupling reaction in which One Monoiodothyronine adds up with Diiodothyronine and forms a new molecule called Triiodothyronine or T3 like wise two Diiodothyronine adds up with another Diiodothyronine to form a an another molecule called Tetraiodothyronine or Thyroxine or T4 ..The newly formed T3 and T4 are called thyroid hormones which are circulating in our blood.after coupling reactions the Thyroglobulin molecule is Cleaved by enzymes into T3 and T4 molecules which are secreated into the Bloodstream after the signal from Pituitary comes in the form of TSH. These Hormones after released in the blood are not fully free they are bound by another protein or serum proteins like TBG Thyroid binding globulin etc only Around 1 % is free of which T3 is more active. T3 and T4 are transported to all the cells which they require.After coming close to the cell membrane of cells T4 is converted into T3 by deiodinase enzymes ,so only T3 enters into the cell for signal transduction, although T4 is main circulating Hormone but inside cells only T3 is taken.. after coming inside the cell Thyroid hormone comes to its receptor in the Nucleus and binds to Thyroid hormone receptor (THR) after that Transcription of the Gene gets started and mRNA gets formed and that mRNA gets transported to Cytoplasm through nuclear pores. In Cytoplasm these mRNA gets translated into Proteins and which later on increases metabolism growth energy etc. Thyroid hormones are regulated from by negative feedback loop mechanism from Hypothalamus to Pituitary and Pituitary to Thyroid Gland In Hypothalamus a factor comes which is called Thyrotropin releasing factor which acts on anterior pituitary to release TSH Thyroid stimulating Hormone (Thyrotropin) which acts on Thyroid Gland to Produce synthesise and secreate Thyroid hormones .If more T3 and T4 are present in blood TSH levels are low and ,if low vice versa.

1. Quantification of Iodine
Ayaz Bashir (JRF)

2. Role of Iodine in Thyroid…
• Iodine is micronutrient required for the
synthesis of Thyroid Hormones.
• In 1896, Bauman determined
association of iodine with Thyroid gland.
• Kendall & Harrington in 1926 described
hormone Complexes using Iodine.
• By 1927 it was described that thyroid
disorders are related to iodine
deficiency.
• Excessive & deficient Iodine levels can
have adverse effects on health.
• Iodine forms: Iodide (I⁻), Molecular
iodine( I₂) and Iodate (IO3̄ ).

3. Metabolism & Absorption
• Iodine absorption takes place in
Stomach & upper small
intestine(Duodenum).
• Iodine gets reduced to Iodide in
Gut before absorption.
• Iodine is absorbed in the form of
Iodide(I⁻).
• I⁻ gets absorbed via an active
transport protein “Sodium-iodide
symporter”(NIS).
• NIS is located on “Apical
Surfaces of Enterocyts”(Intestinal
absorptive cells).
• Iodine absorbed from GIT is
transported to bloodstream.

4. Transport of Iodine
• Iodine is transported in plasma by
loosely binding to plasma
proteins(Albumin).
• Once in the circulation, Thyroid gland
quickly takes up the iodine.
• Iodine in Thyroid gland is taken by ‘’NIS
Transporter’’ which is located on Basal
membrane of Thyroid follicular cells.
• Activity of NIS is three to four times
greater in the thyroid than in any other
tissue in the body.
• This allows the gland to accumulate and
sequester iodide from the blood.
• TSH & Plasma Iodide regulate NIS
expression in T. Follicular cells.

5. Reference
Iodine Intake and Healthy Aging
Leyda Callejas, Shwetha Mallesara and Philip R. Orlander
Division of Endocrinology, Diabetes and Metabolism, University of Texas
Health Science Center, Houston, TX, USA
DOI :
http://dx.doi.org/10.1016/B978-0-12-801816-3.00041-8

6. Methods for determination of Iodine in
Blood &Urine
Methods for Blood
1. Inductively Coupled Plasma/Mass Spectrometry (ICP/MS)
2. Sandel –Kolthoff reaction based
3. Ion-Selective Electrode(ISE)
Methods for Urine
1. Sandell–Kolthoff reaction: Autoanalyzer, Flow Injection, microplate
2. Instrumental neutron activation analysis (INAA)
3. Inductively coupled plasma mass spectrometry (ICP-MS)
4. Electrochemical Detection (ED)
5. Flow injection analysis (FIA)
6. Ion selective electrodes (ISE)
7. Rapid test kit
8. UV–vis spectrometry
9. Kinetic colorimetry
10. Intracavity laser absorbance

7. Title of the Study
A review on Iodine Determination Methods in Salt & Biological Samples.
Corresponding Author:
Mehdi Hedayati
doi no : DOI: 10.5812/scimetr.14092
Lab Address:
Cellular and Molecular Endocrine Research Center, Research institute for Endocrine
Sciences, Shahid Beheshti University of Medical Sciences, Tehran Iran.

8. Details of Study
 In this study different methods for the quantification of Iodine has been determined which are
mentioned in previous slides, out of these methods S-K reaction is most appropriate method for large
number of samples.
 S-K method requires a Spectrophotometric microplate reader, substances interfering with the S-K
reaction usually affect performance, but Chloric acid digestion is an efficient technique for removing
them.
 Despite providing accurate measurements S-K method has some disadvantages too. Despite the high
risk of bias of many included studies , the results suggested the S-K reaction methods to determine
Iodine content.
 S-K method are now technically very simple and have been used by many laboratories to measure
iodine levels for many years.
 ICP-MS method is the most fast, accurate, robust and specific for iodine determination.
 As a result of specificity, ICP-MS is not only a resource for quality assurance, but it is also adaptable for
long-term monitoring of a population’s Iodine status.
 Despite the high cost for instrumentation, the application of ICP-MS may soon become a routine
procedure in clinical chemistry, mainly because of its ability to measure several trace elements
simultaneously.

9. Measurement of Iodine levels in people
Introduction:
• Iodine is a trace mineral that is an essential component of thyroid hormones. Iodine
deficiency can lead to multiple adverse effects on growth and development,
particularly during fetal development and among young children.
• Given the critical role of iodine nutrition in fetal and childhood development, and the
substantial change in iodine status over the last few decades, continued Iodine
monitoring in the populations is an important public health objective.
• More than 90% of iodine consumed is excreted in the urine, making urine iodine a
good indicator of recent iodine intake.
• Collection of urine over 24 hours (µg/day) to quantify urine iodine excretion (UIE) is
often considered the ‘‘reference’’ standard for describing population iodine intake.
• But collection of 24-hour urine samples is expensive and burdensome, large
epidemiologic studies usually collect spot (casual) urine samples.
• The World Health Organization (WHO) currently recommends using the median
urine iodine concentration (UIC; µg/L) from spot urine samples to describe the
iodine status of a population.

10. Continued…
• Urinary Iodine concentration (UIC) is expressed per urine volume, it varies
by recent fluid intake.
• Creatinine, a product of muscle metabolism, is excreted at a relatively
constant rate throughout the day, and therefore has been used as a
correction factor to minimize variation in urine volume.
• The iodine-to-creatinine ratio (I/Cr ratio; µg iodine/g creatinine) has been
considered by some researchers to reasonably estimate 24-hour
UIE(Urinary Iodine Excretion).
• However, WHO describes the use of a creatinine correction factor for iodine
as ‘‘unnecessary’’ and ‘‘unreliable’’. Since creatinine excretion does vary by
sex, age, racial/ethnic background, body mass index, and protein intake.

11. Methods to check iodine levels in Urine & Salt
Method For Urine: UIC / ICP-MS
 UIC is considered a reliable biomarker of recent iodine intake in populations at all
levels.
 More than 90% of ingested iodine is excreted in the urine. A major advantage of UIC
over dietary assessment and household salt consumption data is that UIC represents
the total iodine intake from all dietary sources.
 The concentration of iodine in the urine depends on the urine volume, and the daily
iodine intake can be estimated from spot UIC by estimating the daily UIE.
 Samples are collected as 24 hour and timed spot(Morning, Afternoon, Evening,
Overnight) Urine Iodine samples.
 Urine iodine is analyzed by inductively coupled plasma mass spectrometry (ICP-MS)
 Urine creatinine was analyzed by the Creatinine Plus enzymatic assay on the clinical
analyzer.

12. Method for Salt: ICP-MS
• The testing of household salt samples is usually done with simple rapid test kits.
• A drop of starch-based solution placed onto salt produces a blue/purple color if the
salt contains iodine.
• This approach has clear advantages in iodine monitoring. It is noninvasive, simple,
and inexpensive, and it provides immediate visible results.
• But this approach is inadequate for several reasons. First, RTKs are qualitative not
quantitative; they can detect the presence of iodine in a salt sample, but they cannot
accurately quantify the amount.
• Thus, salt that is not adequately iodized (adequately iodized salt is usually defined as
containing >15 and <40 ppm iodine) will test positive for iodine but will not determine
correct amounts of iodine content present.

13. Continued..
• Salt iodine content can be accurately measured by inductively coupled plasma
mass spectrometry (ICP-MS).
• Unfortunately, only a limited number of laboratories worldwide perform food analysis
with ICP-MS.
• Food composition databases generally contain information on the salt content of
foods, but they rarely specify if the salt used in processed foods is iodized or not.
• In summary, dietary assessment of iodine intake is challenging and the large day-to-
day variation makes it difficult to quantify the “usual” iodine intake. However, dietary
data can be used to identify the most significant food sources of iodine.