Iodine-123 Sodium Iodide Capsules: A Diagnostic Tool for Thyroid Disorders

Iodine-123 Sodium Iodide capsules are a type of radiopharmaceutical used to diagnose various thyroid disorders. The thyroid gland regulates the body’s metabolism, growth, and development. In addition, it produces two primary hormones: thyroxine (T4) and triiodothyronine (T3). These hormones play a crucial role in maintaining optimal body function. As such, detecting and diagnosing thyroid disorders is essential for overall health. I-123 sodium iodide capsules enable clinicians to obtain crucial information about the thyroid’s function and structure, helping them effectively identify and treat thyroid-related conditions.

Iodine-123 Sodium Iodide Capsules: Mechanism of Action

Iodine is a critical component of thyroid hormones T3 and T4. The thyroid gland actively absorbs iodine from the bloodstream to synthesise these hormones. I-123 sodium iodide capsules contain a small amount of radioactive iodine (I-123), which, when ingested, is absorbed by the thyroid gland like non-radioactive iodine. This enables medical professionals to assess the thyroid gland’s function and structure using imaging techniques such as gamma cameras and single-photon emission computed tomography (SPECT).

Applications of Iodine-123 Sodium Iodide Capsules in Thyroid Disorder Diagnosis

Iodine-123-123 sodium iodide capsules are primarily used for diagnostic purposes, such as in thyroid scintigraphy or thyroid uptake tests. These tests help evaluate thyroid function and detect various thyroid disorders, including hyperthyroidism, hypothyroidism, thyroid nodules or cancers. The main applications of I-123 sodium iodide capsules include the following:

  • Thyroid Scintigraphy involves using a gamma camera to capture images of the thyroid gland after administering I-123 sodium iodide capsules. The radioactive iodine absorbed by the thyroid gland emits gamma rays, which are detected by the camera, producing detailed images of the gland’s structure and function. These images help identify abnormal thyroid tissue, nodules, or tumours.
  • Thyroid Uptake Test measures the amount of radioactive iodine absorbed by the thyroid gland over a specific period, usually 4-6 hours and 24 hours after capsule administration. The results are expressed as a percentage of the total radioactive iodine administered, known as the thyroid uptake value. Higher or lower uptake values may indicate hyperthyroidism or hypothyroidism, respectively.

Advantages and Safety

I-123 sodium iodide capsules offer several advantages over radioactive isotopes, such as Iodine-131. I-123 has a short half-life (approximately 13 hours), which reduces radiation exposure and allows for quicker test results. Additionally, I-123 emits gamma rays with lower energy levels than I-131, minimising the risk of radiation damage to the thyroid gland and surrounding tissues. I-123 Sodium iodide capsules are considered safe, with minimal side effects and low radiation exposure.


I-123 sodium iodide capsules are a valuable diagnostic tool for detecting and evaluating thyroid disorders. By providing vital information about the thyroid gland’s function and structure, these capsules enable healthcare professionals to make informed decisions regarding diagnosing and treating thyroid-related conditions. As medical technology advances, I-123 sodium iodide capsules will continue to play a significant role in effectively managing thyroid disorders.

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Tags: Differentiated Thyroid Cancer, Radiopharmaceuticals
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