Iodine-125 Iothalamate: Diagnostic Imaging and Renal Function

Iodine-125 Iothalamate is a radiolabelled contrast agent used in diagnostic imaging. It is characterised by its ability to bind with plasma proteins and its relatively low radiation exposure, making it an ideal choice for specific imaging procedures. This article briefly overviews I-125 iothalamate, its applications, advantages, and potential associated risks.

Iodine-125 iothalamate is a water-soluble, iodinated compound incorporated into its structure with a radioactive isotope, iodine-125. It is primarily used as a radiotracer in renal function tests, specifically for measuring the glomerular filtration rate (GFR), which is crucial in assessing kidney function. The agent is administered intravenously, and its concentration in blood and urine samples is measured over time to calculate GFR.

Iodine-125 Iothalamate: A Safe and Cost-effective Radiotracer for Accurate GFR Measurement and Kidney Function Analysis

  • I-125 iothalamate has a high affinity for plasma proteins, mainly albumin. This characteristic ensures that the agent remains within the vascular compartment, enabling more accurate measurement of GFR.
  • Iodine-125 is a gamma-emitting isotope with a relatively long half-life of 59.4 days. The low-energy gamma radiation (27-35 keV) emitted by I-125 reduces radiation exposure to patients and medical personnel compared to other isotopes, such as technetium-99m.
  • Iodine-125 iothalamate is stable both in vitro and in vivo, ensuring the agent maintains its integrity and remains bound to plasma proteins throughout the diagnostic procedure.
  • I-125 iothalamate is readily available and relatively affordable compared to other radiotracers, making it a cost-effective choice for healthcare providers.

Iodine-125 Iothalamate: Precautions, Allergic Reactions, and Potential Interference in Diagnostic Procedures

  • As with any iodinated contrast agent, there is a risk of allergic reactions to I-125 iothalamate ranging from mild to severe. Patients with a history of allergy to iodine or iodinated contrast agents should be closely monitored during the procedure.
  • Although the radiation exposure associated with I-125 iothalamate is relatively low, it is still radioactive. Pregnant or breastfeeding women should avoid undergoing procedures involving I-125 iothalamate to minimise radiation exposure to the fetus or infant.
  • I-125 iothalamate can interfere with other diagnostic tests involving iodine, such as thyroid function tests. Appropriate precautions should be taken to avoid false results.


Iodine-125 iothalamate is a valuable diagnostic tool in evaluating renal function due to its high protein binding, low radiation exposure, and cost-effectiveness. However, potential risks and limitations should be considered and managed appropriately to ensure this radiotracer’s safe and accurate use in clinical practice.

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