Serum Iodine

Serum iodine testing evaluates iodine status during pregnancy. Iodine deficiency can lead to complications such as hypothyroidism and impaired neurodevelopment. This article explores the importance of serum iodine testing, recommended reference ranges, and common causes of deficiencies.

Serum Iodine Testing

The iodine, serum, or plasma test (also known as the serum iodine concentration, or SIC, test) analyzes the amount of iodine present in a blood sample. It represents the iodide pool. 

Iodine, serum, or plasma testing is less commonly used in research to assess iodine deficiency. The more common measure is urinary iodine clearance. Studies show that the iodine, serum, or plasma test accurately correlates with the UIC:creatinine ratio.

Iodide is absorbed through the stomach and small intestines, with between 70% and 90% of dietary iodide being absorbed. Iodine absorption is lower and may vary depending on other factors, as it is not naturally found in the diet as iodine.

Once absorbed, iodide enters the bloodstream and becomes part of the iodide pool. The iodide pool is the serum-accumulated iodide that the body can pull from. This can be recycled iodide from the deiodination of thyroxine as well as recent intake.

Serum Iodine in Pregnancy

During pregnancy, there is a 50% increase in the dietary need for iodine. Much of the iodine is used to increase maternal thyroid hormone production. Another portion of iodine is transferred to the fetus for storage, starting around 10 to 12 weeks of gestation until the fetus begins producing its own thyroid hormones at around 16 to 20 weeks. Iodine is also essential for developing the fetal brain and nervous system.

Iodine absorption and clearance are increased during pregnancy.

High Serum Iodine in Pregnancy

Elevated serum iodine levels, particularly in the first trimester, may have a slight negative impact on motor and physical development and infant intellect, according to a 2024 study.

It has been suggested that excess iodine in the first trimester may be a cause of nausea as a means of preventing excess consumption. Pregnancy nausea is closely linked to iodine intake and thyroid function.

Most Common Causes of High Serum Iodine in Pregnancy

• ​Iodine Overdose
• Nutritional Deficiencies (magnesium)
• Kidney Disease
• Goitrogen Exposure
• Contaminated Water
• Oxidative Stress

Low Serum Iodine in Pregnancy

In the US, between 2011 and 2021, 38% of the population was classified as iodine deficient.
A 2021 sampling of pregnant women in Michigan found that 23% had inadequate iodine intake.

It is estimated that an average of 44% of Europeans are iodine deficient, and more than 50% of those in central and western Europe are deficient.

A 2011 study from Spain found that only 14.4% of pregnant women in the first trimester and 26.8% in the second trimester had adequate iodine levels.

In Southeast Asia and the Eastern Mediterranean, iodine deficiency is estimated to affect 36% to 43% of the general population.

Serum iodine levels are associated with urinary iodine clearance (UIC) and thyroid function in pregnancy. Low serum iodine is associated with an increased risk for iodine deficiency and hypothyroxinemia.

Maternal iodine deficiency in pregnancy is associated with childhood cognitive
delays, lower IQ, and increased learning disabilities in children.

Most Common Causes of Low Serum Iodine in Pregnancy

• Iodine Deficient Diet
• Nutritional Deficiencies (vitamin A)
• Inflammatory Bowel Diseases (Celiac Disease)
• Certain Medications (Lithium, Diuretics)
• Environmental Chemical Exposure

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Medical Disclaimer:
This content is for educational purposes only and is intended for licensed medical professionals. It is based on current research, subject to change, and not intended to diagnose, treat, or prevent any medical condition. This information does not replace consultation with a qualified healthcare provider. Seek professional medical evaluation and treatment from a licensed provider. Use of this information is at your own risk.​

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