A new case study published in the Canadian Medical Association Journalfound that in rare cases, children can develop food allergies after receiving blood transfusions.

While children are often vulnerable to allergic reactions, these children were sensitized only after they got a transfusion of blood products.

Between 1 and 10 percent of children have food allergies, and that number is on the rise. The most common enemies are milk, eggs, and peanuts. 

The case study centers on an 8-year-old boy who had no history of allergies. After receiving craniospinal radiation and a blood transfusion, the boy experienced an anaphylactic reaction within 10 minutes of eating salmon and ended up in the hospital.


What surprised doctors was that the boy had eaten salmon before without allergic reaction. Four days after the fish-induced reaction, the boy experienced an allergic reaction to a peanut butter cup, even though he had eaten peanut products before.

“We were surprised to find that this young boy acquired multiple food allergies and reacted to more than one food,” said study co-author Dr. Julia Upton, a lecturer in the department of pediatrics at the University of Toronto. 

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The 8-year-old’s experience drew the attention of Canadian Blood Services, which investigated the event. It turns out that, for children, a passive transfer of allergies through a blood transfusion is possible. 

One donor of blood products to the boy had a severe allergy to peanuts, tree nuts, shellfish, and all fish, including salmon. That donor was excluded from future donations. After about four months, the boy’s allergic reactions disappeared.

The case highlights several key points, including that unusual causes of food allergies should be suspected in children who react to previously tolerated foods. Another is that reporting the suspected passive transfer of allergies can help make everyone safer.

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“It is a misconception that food allergy can be diagnosed based on blood testing or skin testing alone. It is important to know that the diagnosis of food allergy involves many parts,” Upton said. 

A difficulty in diagnosing allergies is that reactions can differ from person to person and trigger to trigger.

“For example, the history of what happened when the food was eaten is very important. Other allergies, such as pollen allergies, can change the way we interpret skin and blood tests,” Upton said. 

Researchers say it’s important that parents and caretakers understand the signs of allergies, such as facial swelling, throat discomfort, and sudden fatigue. These symptoms should be treated immediately, and the child should be taken to the emergency room. 

“The field of allergy is moving quickly,” Upton said. “It is best to discuss suspected food allergies with a physician knowledgeable about allergy.” 

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