Answer to Question #3823 Submitted to "Ask the Experts"

My wife is working at a hospital laboratory with radioimmunoassay using ¹²⁵I in its tests. There appear to be no health-protection practices at the hospital. She is working eight hours at the laboratory. What kind of risks does she have?

RIA or radioimmunoassay kits are commonly used for in vitro clinical and laboratory tests. They contain very small amounts of radioactive ¹²⁵I or could be another radionuclide. The amount of radioactivity used in the kits is limited by the Nuclear Regulatory Commission (NRC) to no more than 10 microcuries of ¹²⁵I apiece, and the permissible quantities of other radionuclides would have similarly low activity limits. Since the radioactive quantities are so small, the RIA kits are considered "generally licensed" radioactive material. This means that they can be ordered and received by any physician, veterinarian, clinical laboratory, or hospital without the need for a specific and more restrictive radioactive material license through the NRC or Agreement State. That is not to say any regulatory and registration requirements are not required. General licensees are still regulated by the NRC and need to complete certain registration forms.

The NRC has evaluated and considers that the potential radiation exposure from these kits to be less than 2% of the allowable annual dose for a radiation worker¹. Generally, exposures of more than 100 millirem is the trigger at which radiation safety training and other requirements are required. Thus, due to the small risk, the RIA kits are exempt from the typical specific license requirements for radiation safety training, exposure monitoring, contamination monitoring, security of sources, inventory control, and disposal as radioactive waste, all of which is required for greater quantities of radioactive material.

If this apparent lack of regulatory protection, which is based on the evaluation that these kits are an insignificant radiation hazard, is not enough to reassure you or your wife, a review of the kit's Material Safety Data Sheet (MSDS) can offer more reassurance. Universal precautions designed to minimize internal uptake are the only protections recommended².

Cathy Ribaudo

Editor’s Note:
¹Radiation exposure to radiation workers is to be limited to 5,000 mrem per year. Thus, 2% of the allowable limit would be 100 mrem, which is the exposure limit for members of the public. It should be noted that the background exposure from natural radiation sources to members of the public is 360 mrem per year.

²An MSDS of a typical RIA kit can be found at the Linco Research, Inc., website.