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Iodine Deficiency Workup

  • Author: Stephanie L Lee, MD, PhD; Chief Editor: George T Griffing, MD  more...
 
Updated: Dec 16, 2015
 

Approach Considerations

There has been particular interest in monitoring iodine sufficiency in pregnant women and school-aged children. These populations are important, because they are easily accessible and are particularly vulnerable to the adverse effects caused by iodine deficiency.

Surveillance techniques to monitor iodine sufficiency in a population include assessment of thyroid volume, urinary iodine concentration, dried whole-blood spot thyroglobulin (Tg) levels, and dietary questionnaires; the last method is the least reliable. No test that can reliably diagnose iodine deficiency in individual patients is available.

Results from thyroid function studies are usually within the reference range in the presence of mild iodine insufficiency. However, in patients with euthyroidism and iodine deficiency, serum TSH levels may be normal to increased, T3 levels may be normal or slightly elevated, and T4 levels may be normal or decreased. Only in very extreme iodine deficiency does hypothyroidism develop, accompanied by an elevated serum TSH value and decreased T3 and T4 levels.

Population studies have shown that newborns with iodine deficiency disorder (IDD) have elevated TSH levels at birth that normalize when evaluated again several weeks later. The extent of their transient hypothyroidism correlates with the severity of the iodine deficiency.

Measurement of a dried whole-blood spot level of Tg can be a useful indicator of the thyroid function in children and may be a more sensitive early measure of iodine repletion than serum TSH or thyroxine (T4).[18] International reference standards have recently been established for serum thyroglobulin values in school-aged children.[19] Current limitations to the use of dried blood spot Tg measurements include assay complexity and the unknown utility of measuring antithyroglobulin antibody levels in children.

Imaging studies

The 24-hour radioactive iodine uptake value is increased substantially in the presence of iodine deficiency disorder because of increased TSH stimulation and reduction in the nonisotopic iodine pool. Therefore, thyroid uptake values in iodine-sufficient areas, such as the United States, are significantly lower than in areas with iodine deficiency, as in many regions of Europe.

Thyroid size estimated on ultrasonograms has been shown to reflect the iodine sufficiency of a population. When goiter appears in more than 5% of a regional population, iodine deficiency should be considered.[20]

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Urinary Iodine Evaluation

The kidneys excrete approximately 90% of ingested iodine. Therefore, the best diagnostic test to identify IDD in a population is a median 24-hour urine iodine collection. If a 24-hour urine collection is not practical, a random urinary iodine-to-creatinine ratio can be used instead. In this case, a median of 50-100 mcg of iodine per liter is consistent with mild iodine deficiency, 20-49 mcg of iodine per liter is consistent with moderate deficiency, and less than 20 mcg of iodine per liter is consistent with severe deficiency.

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Histologic Findings

In young patients with iodine deficiency, the usual finding is diffuse hyperplasia of the thyroid gland. Histologically, extreme hyperplasia can be seen with little or no colloid, as shown in the image below.

Histologic sections from a normal thyroid and from Histologic sections from a normal thyroid and from an endemic goiter that was removed because of compressive symptoms. The normal thyroid (A) contains thyroid cells arranged in a monolayered sheet around a storage form of thyroid hormone, colloid, while the endemic goiter (B) shows intense hyperplasia with no colloid. Image courtesy of F. DeLange.

With aging, the diffuse goiter of iodine deficiency becomes more nodular. Histologically, the nodular goiter develops from areas of hyperplasia separated by areas of degeneration and fibrosis. In older patients, the thyroid gland tends to be extremely heterogeneous, with colloid-containing vesicles, hyperplastic areas, degenerating areas, and fibrosis.

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Contributor Information and Disclosures
Author

Stephanie L Lee, MD, PhD Associate Professor, Department of Medicine, Boston University School of Medicine; Director of Thyroid Health Center, Section of Endocrinology, Diabetes and Nutrition, Boston Medical Center; Fellow, Association of Clinical Endocrinology

Stephanie L Lee, MD, PhD is a member of the following medical societies: American College of Endocrinology, American Thyroid Association, Endocrine Society

Disclosure: Nothing to disclose.

Coauthor(s)

Elizabeth N Pearce, MD, MSc Associate Professor of Medicine, Boston Medical Center, Boston University School of Medicine

Elizabeth N Pearce, MD, MSc is a member of the following medical societies: American Association of Clinical Endocrinologists, American Thyroid Association, Endocrine Society, Massachusetts Medical Society

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: consulted for Scientific Consulting Company GmbH; advisory board for Endocrine Advisor Website; Member of the Management Council of the Iodine Global Network.

Sonia Ananthakrishnan, MD Assistant Professor of Medicine, Section of Endocrinology, Diabetes and Nutrition, Boston Medical Center, Boston University School of Medicine

Disclosure: Nothing to disclose.

Chief Editor

George T Griffing, MD Professor Emeritus of Medicine, St Louis University School of Medicine

George T Griffing, MD is a member of the following medical societies: American Association for the Advancement of Science, International Society for Clinical Densitometry, Southern Society for Clinical Investigation, American College of Medical Practice Executives, American Association for Physician Leadership, American College of Physicians, American Diabetes Association, American Federation for Medical Research, American Heart Association, Central Society for Clinical and Translational Research, Endocrine Society

Disclosure: Nothing to disclose.

Acknowledgements

Arthur B Chausmer, MD, PhD, FACP, FACE, FACN, CNS Professor of Medicine (Endocrinology, Adj), Johns Hopkins School of Medicine; Affiliate Research Professor, Bioinformatics and Computational Biology Program, School of Computational Sciences, George Mason University; Principal, C/A Informatics, LLC

Arthur B Chausmer, MD, PhD, FACP, FACE, FACN, CNS is a member of the following medical societies: American Association of Clinical Endocrinologists, American College of Endocrinology, American College of Nutrition, American College of Physicians, American College of Physicians-American Society of Internal Medicine, American Medical Informatics Association, American Society for Bone and Mineral Research, Endocrine Society, and International Society for Clinical Densitometry

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

References
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Distribution of iodine deficiency in developing countries.
Typical endemic goiters in 3 women from the Himalayas, an area of severe iodine deficiency. Image courtesy of F. DeLange.
A man and 3 females (age range, 17-20 y) with myxedematous cretinism from the Republic of the Congo in Africa, a region with severe iodine deficiency. Image courtesy of F. DeLange.
Histologic sections from a normal thyroid and from an endemic goiter that was removed because of compressive symptoms. The normal thyroid (A) contains thyroid cells arranged in a monolayered sheet around a storage form of thyroid hormone, colloid, while the endemic goiter (B) shows intense hyperplasia with no colloid. Image courtesy of F. DeLange.
Table.
Iodine Deficiency None Mild Moderate Severe
Median urine iodine, mcg/L >100 50-99 20-49 < 20
Goiter prevalence < 5% 5-20% 20-30% >30%
Neonatal thyroid-stimulating hormone (TSH),



>5 IU/mL whole blood



< 3% 3-20% 20-40% >40%
Cretinism 0 0 + +
Adapted from the World Health Organization (WHO)/United Nations Children's Fund (UNICEF)/International Council for Control of Iodine Deficiency Disorders (ICCIDD).
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