Glossary

Irradiation

Modification to a blood product in which cellular blood products are exposed to a specified amount of either gamma rays, x-rays, or ultraviolet B rays (outside of the U.S.). Irradiation is performed solely to prevent transfusion-associated graft vs. host disease, a horrible complication of transfusion that is far better prevented than diagnosed. In order for a product to be called “irradiated” in the U.S., 25 Gray (Gy) of irradiation is targeted to the center of the blood product, with the equipment calibrated to deliver no less than 15 Gy to any part of the bag (the dose is higher in other countries, up to a maximum of 50 Gy).

Note that the number and units for irradiation can vary depending on who you read. Some sources use the term “centiGray” rather than “Gray,” and the minimum dose requirement changes from “25 Gy” to “2500 cGy.” Even worse, some people still use the term “rad” to describe the units of irradiation, and “rad” is the same as “cGy.” So, if you are a learner, be prepared to switch back and forth, because you could see any of the units on exams. To summarize, in the U.S., the targeted dose to the center of the blood product may be written as: 25 Gy (“25 Gray”), 2500 cGy (2500 “centiGray”), or 2500 rad. 

This procedure can be done either at the collecting facility (blood center) or transfusion service. Many facilities have stand-alone cesium-based irradiators that they use to perform the procedure, but in recent years, their use has become much more regulated and logistically challenging. Stand-alone X-ray irradiators have become much more popular in recent years, as they have fewer administrative and regulatory headaches (but some report more maintenance challenges with those systems). Some hospitals utilize the linear accelerators used in radiation oncology therapy to irradiate blood products.

The FDA says that an irradiated product expires 28 days from irradiation OR the product’s regular expiration date, whichever comes first. Obviously, irradiating a unit of platelets has no effect whatsoever on that unit’s expiration time (since platelets only have a five day shelf-life anyway). See the “Why do we irradiate?” video for more information.

For more on irradiation, see episode 074CE of the Blood Bank Guy Essentials Podcast.

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