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Urinary Iodine Excretion – Meaning and Reference Values

Urinary iodine excretion measures the amount of iodine the body eliminates through urine and is the key biomarker for assessing iodine status and nutritional iodine intake.

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Things worth knowing about "Urinary Iodine Excretion"

Urinary iodine excretion measures the amount of iodine the body eliminates through urine and is the key biomarker for assessing iodine status and nutritional iodine intake.

What Is Urinary Iodine Excretion?

Urinary iodine excretion (UIE) refers to the amount of iodine that the human body eliminates, primarily through the urine. Because the kidneys filter and excrete excess iodine efficiently, urinary iodine concentration directly reflects recent dietary iodine intake. For this reason, UIE is the most widely used biomarker to assess iodine status in both individuals and populations.

Biological Background

Iodine is an essential trace element required for the synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolism, growth, and neurological development. Dietary iodine is almost completely absorbed in the small intestine and transported via the bloodstream to the thyroid gland and other tissues. Any iodine not taken up by the thyroid is filtered by the kidneys and excreted in the urine.

Measuring Urinary Iodine Excretion

Methods

Spot urine sample: Iodine concentration is measured in a single urine sample, often expressed relative to creatinine (µg iodine per g creatinine). This practical method is widely used in population-based studies.
24-hour urine collection: Considered the gold standard for individual assessment. All urine produced over 24 hours is collected, allowing precise quantification of total iodine excreted.

Reference Values

The World Health Organization (WHO) has established reference ranges for median urinary iodine concentration to classify iodine status in population groups:

Below 100 µg/l: Iodine deficiency (mild, moderate, or severe depending on level)
100–199 µg/l: Adequate iodine intake (general adult population)
150–249 µg/l: Adequate iodine intake (pregnant women)
Above 300 µg/l: Possible excessive iodine intake

Clinical Relevance

Iodine Deficiency

A low urinary iodine excretion indicates insufficient dietary iodine intake. Iodine deficiency can lead to enlargement of the thyroid gland (goiter), underactive thyroid (hypothyroidism), and – particularly during pregnancy – serious developmental disorders in the child, including impaired cognitive development.

Excessive Iodine Intake

Persistently elevated urinary iodine levels may also have negative health consequences, as excessive iodine can trigger or worsen thyroid conditions such as Hashimoto thyroiditis or Graves disease. Individuals with pre-existing thyroid disorders should have their iodine intake medically monitored.

At-Risk Groups

Pregnant and breastfeeding women (increased iodine requirements)
Vegans and vegetarians (reduced iodine intake due to avoidance of dairy and fish)
Populations in iodine-poor regions (e.g., inland areas with limited seafood consumption)

Factors Influencing Urinary Iodine Excretion

Several factors can affect iodine excretion levels:

Diet: Iodine-rich foods such as seafood, fish, dairy products, and iodized salt increase urinary iodine concentrations.
Iodinated contrast agents: Radiological contrast media containing iodine can massively and transiently elevate urinary iodine excretion.
Medications: Certain drugs such as amiodarone (a cardiac medication) contain large amounts of iodine and significantly affect excretion levels.
Dietary supplements: Iodine supplements or products derived from seaweed and algae can substantially raise urinary iodine concentrations.
Kidney function: Impaired renal function may reduce the ability to excrete iodine effectively.

References

World Health Organization (WHO), UNICEF, ICCIDD: Assessment of Iodine Deficiency Disorders and Monitoring their Elimination. 3rd edition, WHO Press, Geneva, 2007.
Zimmermann MB: Iodine deficiency. Endocrine Reviews, 2009; 30(4):376–408. PubMed PMID: 19460960.
Pearce EN, Andersson M, Zimmermann MB: Global iodine nutrition: Where do we stand in 2013? Thyroid, 2013; 23(5):523–528. PubMed PMID: 23472655.

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