Glossary

Urticarial Transfusion Reaction

Also known as a “mild allergic” transfusion reaction, this is one of the most common adverse events reported as a consequence of blood transfusion. Urticarial reactions are reported in roughly 1% of transfusions (and are almost certainly under-reported). In general, these reactions occur as a result of a pre-formed, recipient IgE antibody that reacts against something in the transfused blood product, most commonly a donor plasma protein. This results in a “type I hypersensitivity” reaction, where histamine and other substances are released from mast cells and basophils through interaction with IgE. The secretions result in the formation of pruritic (itchy), raised, red-rimmed “wheals” on the skin of the recipient.

In most cases, urticarial reactions are simple to diagnose and do not cause significant problems for the patient (though they can be terrifying for the patient, so please don’t discount them as completely benign!). They are treated with an antihistamine such as diphenhydramine (Benadryl). Most blood banks allow providers to stop the transfusion when a mild allergic reaction is seen, treat the patient, then resume the transfusion when the rash clears. In most cases, someone who has an urticarial reaction will not progress to having a more severe allergic (i.e., anaphylactic) reaction, but such progression can definitely occur.

For more on these reactions, and why premedication with diphenhyramine doesn’t necessarily help, please check out episode 024 of the Blood Bank Guy Essentials Podcast.

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