Iodine-131 Sodium Iodide: Thyroid Disorder Diagnosis and Treatment

Iodine-131 sodium iodide (NaI-131) is a radioactive isotope of iodine used in various medical applications, such as diagnosing and treating thyroid disorders and specific cancer therapies. This compound consists of a radioactive isotope, iodine-131 (I-131), combined with sodium iodide, forming a radiopharmaceutical that is absorbed by thyroid cells when ingested.

Iodine-131 has a half-life of approximately eight days, meaning it decays into other isotopes over time, emitting beta particles and gamma radiation. This article will explore the medical applications, mechanism of action, and risks associated with iodine-131 sodium iodide.

Iodine-131 sodium iodide is frequently used in a diagnostic test called a radioactive iodine uptake (RAIU) test. This test measures the thyroid gland’s ability to absorb iodine, providing crucial information about thyroid function. It is often used to diagnose hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), and other thyroid-related conditions.

Iodine-131 sodium iodide can be used to treat hyperthyroidism by reducing the activity of the thyroid gland. The treatment, known as radioactive iodine therapy (RAI), involves administering a carefully calculated dose of NaI-131, which is then absorbed by the thyroid gland. The beta particles emitted by I-131 destroy the overactive thyroid cells, reducing thyroid hormone production and alleviating hyperthyroid symptoms.

Thyroid cancer treatment: NaI-131 is also used to treat certain types of thyroid cancer, especially those that have spread to other parts of the body (metastatic thyroid cancer). The cancerous thyroid cells absorb the radioactive iodine, and the emitted beta particles destroy these cells. This targeted therapy can help shrink tumours and prevent the spread of cancer cells.

Iodine-131 sodium iodide’s mechanism of action is primarily based on the selective uptake of iodine by the thyroid gland. Once ingested, NaI-131 is absorbed by the gastrointestinal tract and enters the bloodstream. The thyroid gland selectively absorbs iodine from the blood and incorporates it into thyroid hormones. When the radioactive iodine-131 isotope is present, it emits beta particles that destroy thyroid cells. This targeted effect allows for treating thyroid disorders and cancer with minimal damage to surrounding tissues.

Risks and Side Effects of Iodine-131 Sodium Iodide in Thyroid Diagnosis and Treatment

While iodine-131 sodium iodide has proven effective in diagnosing and treating thyroid disorders and cancer, it is not without risks and side effects. Some potential risks and side effects include:

  • As a radioactive substance, I-131 emits radiation, which can pose a risk to the patient and those around them. However, the short half-life of I-131 (8 days) and the targeted nature of the therapy help minimize these risks.
  • A potential side effect of radioactive iodine therapy is hypothyroidism, which occurs when the thyroid gland becomes underactive. Patients may require lifelong thyroid hormone replacement therapy to manage this condition.
  • Iodine-131 sodium iodide is contraindicated in pregnant and breastfeeding women, as it can harm the developing fetus or infant.


Iodine-131 sodium iodide is a valuable tool in diagnosing and treating thyroid disorders and cancer. Its targeted mechanism of action allows for effective treatment with minimal damage to surrounding tissues. The short half-life of I-131 and the selective uptake of iodine by the thyroid gland contribute to the safety and efficacy of this radiopharmaceutical. However, it is essential to consider potential risks and side effects, such as radiation exposure, hypothyroidism, and contraindications during pregnancy and breastfeeding. As a result, careful patient selection, monitoring, and follow-up are crucial to ensure optimal outcomes for those undergoing treatment with iodine-131 sodium iodide.

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Tags: Differentiated Thyroid Cancer, Dosimetry, Radiopharmaceuticals
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