Donated blood is routinely screened for dangerous pathogens – things like HIV and Hepatitis – to make sure there is no threat to the recipient’s health during a transfusion. But a case study just published in The New England Journal of Medicine suggests that viruses are not the only hazards lurking in the collection bag.

The authors of the paper, a physician team from The Netherlands, reported that during a blood transfusion, the 6-year-old recipient suddenly burst out in a rash and started having difficulty breathing. Recognizing the boy was having an anaphylactic reaction, the doctors rescued him with a syringe of adrenaline.

The patient was definitely allergic to something, but quick tests showed that it was not due to latex glove sensitivity or an adverse reaction to a drug. Upon questioning, the boy’s mother recalled that he had a similar reaction after eating a few peanuts a few years back.

Immediately, the doctors began testing the boy’s blood, to see if he had antibodies to the peanut peptides circulating through his body, a measure that would determine if he had been exposed to the allergen that had made him sick in the past. Though his mother confirmed that he had not eaten a peanut in 5 years, the level of peanut peptide antibodies in his body was 200x higher than normal.

The doctors started to wonder: Could the blood the boy received somehow been tainted with peanut allergens?

While the peanut protein is rapidly digested, a 2009 study found that one of the legume’s smaller peptides, Ara h2, can stay in the bloodstream and saliva for up to 24 hours after eating. And confirming their suspicions, 3 out of 5 of the donors who contributed to bag of blood the boy received recalled snacking on several handfuls of peanuts the night before they donated.

Most hospitals tell donors to eat breakfast before arriving at the clinic, but they do advise people to stay away from certain foods – fatty grub like burgers, fries, and ice cream – that can interfere with the standard tests that labs use to make sure the blood isn’t infected. And while allergic reactions to blood transfusions are rare, the solution may be simple. Shouldn’t we at least consider adding peanuts to the list of foods people should avoid before donating blood?

Photo via Flickr

Brian Mossop is currently the Community Editor at Wired, where he works across the brand, both magazine and website, to build and maintain strong social communities. Brian received a BS in Electrical Engineering from Lafayette College, and a PhD in Biomedical Engineering from Duke University in 2006. His postdoctoral work was in neuroscience at UCSF and Genentech.

Brian has written about science for Wired, Scientific American, Slate, Scientific American MIND, and elsewhere. He primarily cover topics on neuroscience, development, behavior change, and health.

Contact Brian at brian.mossop@gmail.com, on Twitter (@bmossop), or visit his personal website.