Iodine-125 Human Serum Albumin: A Radiolabelled Diagnostic Agent

Iodine-125 is a radioisotope of iodine with a half-life of approximately 59.4 days, emitting low-energy gamma rays that gamma cameras can easily detect. Human serum albumin (HSA) is the most abundant protein in human blood plasma, playing a crucial role in maintaining the colloidal osmotic pressure and transporting various substances. Therefore, the combination of Iodine-125 and Human Serum Albumin, I-125 HSA, has been utilised in various medical applications, particularly as a diagnostic radiopharmaceutical agent. This article discusses the properties, applications, and safety concerns of I-125 HSA.

Properties of Iodine-125 Human Serum Albumin

I-125 HSA is a radiolabelled compound created by attaching the I-125 isotope to HSA. The low-energy gamma rays emitted by I-125 allow for non-invasive imaging, while HSA’s high affinity for binding with various molecules and its biocompatibility makes it an ideal carrier. In addition, the biodistribution of I-125 HSA is similar to that of non-radiolabelled HSA, ensuring that the compound remains within the vascular system and does not accumulate in organs or tissues.

Blood Volume Measurement, Vascular Permeability Assessment, and Protein-Losing Gastroenteropathy

  • Blood Volume Measurement: I-125 HSA is frequently used to measure blood volume, particularly in patients with heart failure, kidney diseases, or other conditions that affect blood volume. The radiolabelled HSA is injected into the patient’s bloodstream, and its distribution is assessed using gamma cameras. This technique allows clinicians to accurately determine blood volume, providing valuable information for diagnosis and treatment planning.
  • Vascular Permeability Assessment: I-125 HSA is employed to evaluate the permeability of blood vessels in various pathological conditions, such as inflammation or tumours. The radiolabelled compound is injected, and its leakage from the vascular system is monitored over time. The increased permeability may indicate the presence of disease or injury, which can be further investigated and treated accordingly.
  • Protein-Losing Gastroenteropathy Evaluation: I-125 HSA can be utilised to identify abnormal protein loss through the gastrointestinal tract. Patients with suspected protein-losing gastroenteropathy are administered I-125 HSA, and faecal samples are collected over several days. Increased radioactivity in the faeces indicates excessive protein loss, allowing for accurate diagnosis and targeted treatment.

I-125 HSA in Diagnostic Procedures: ALARA Principles and Patient Safety through Rigorous Screening

While I-125 HSA is generally considered safe for diagnostic procedures, there are some potential risks. Patients are exposed to ionising radiation, albeit at low levels, as with any radiopharmaceutical. Therefore, the risk of radiation exposure must be weighed against the diagnostic benefits, with the principle of ALARA (As Low As Reasonably Achievable) being applied. Additionally, as HSA is derived from human blood, infectious agents are less likely to be transmitted. However, stringent screening and purification processes have significantly reduced this risk.


Iodine-125 Human Serum Albumin has proven to be a valuable diagnostic tool in various medical applications, such as blood volume measurement, vascular permeability assessment, and protein-losing gastroenteropathy evaluation. While some safety concerns exist, the benefits of using I-125 HSA often outweigh the risks, making it an essential component in modern diagnostic medicine.

Tags: Radiopharmaceuticals
Open Medscience