In rare cases, children can develop anaphylactic allergies¹ to previously² tolerated foods after receiving blood products via transfusion³, report the authors of a case study published in CMAJ (Canadian Medical Association Journal). "It is very unusual to identify someone who experienced passive transfer of allergy⁴ from blood products," says Dr. Julia Upton, The Hospital for Sick Children (SickKids), Toronto, Ontario. "Importantly, this condition has an excellent prognosis and typically resolves within a few months. Blood donors⁵ who have food allergies can transfer immunoglobulin E, an antibody that reacts against allergens, from blood products such as platelets. This is rare."

It is important for parents and physicians to be aware of this event in case children have anaphylactic reactions after receiving blood products, particularly after eating peanuts, tree nuts and fish, foods that they could previously consume without reaction. These reactions -- with symptoms such as facial swelling⁶, throat discomfort⁷ or sudden fatigue⁸ -- should be treated immediately at an emergency department.

When there is passive transfer of allergies after blood transfusion, physicians should follow up with the family after a few months to decide the timing⁹ of careful reintroduction of the temporary allergens into a child's diet.

It is also important for physicians to report suspected cases of passive transfer of allergies to the hospital's transfusion service to investigate the cause and ensure the safety of the country's blood supply.