The unidentified boy developed temporary food allergies after receiving a range of blood products.
In the span of a few days, two foods he had eaten often in the past sent him to the emergency department.
Doctors at the hospital suspected he had been sensitized to the foods through the blood transfusions. A trace back of the blood products revealed that one of the donors had severe allergies to peanuts, tree nuts, shellfish and other fish.
The boy had had no known allergies before receiving the blood transfusions. But a skin scratch test revealed he reacted to the same foods as his blood donor did.
Salmon and a peanut butter cup are what sent him to hospital.
"His parents were very surprised because they could give a very clear history of repeatedly and commonly eating fish and peanuts. So it was very surprising that he then had these reactions. And it was that history that led us to think about: Could there be an unusual cause here?" said Dr. Julia Upton, an allergist-immunologist at the hospital.
Upton is the senior author of a case report on the incident published Tuesday in the Canadian Medical Association Journal.
She said doctors should be aware that reactions to previously tolerated foods are rare and may have an unusual cause. She also suggested reintroduction of foods after an event like this should be done with medical supervision.
In this case, tests revealed the boy had IgE — an antibody that signals an allergic reaction — in his blood after he reacted to the foods. The theory is he acquired the antibody through the blood transfusion.
The hospital told the boy's parents the IgE would probably clear from his blood over time. And that is what happened. The foods he reacted to have been reintroduced into his diet without further reactions.
Canadian Blood Services said this isn't the first time this phenomenon has been seen. In fact, the first known case was reported in 1919.
But such events are rare and this is only the second in Canada in the past decade, said Dr. Mindy Goldman, the agency's medical director.
Goldman said Canadian Blood Services asks potential blood donors if they are experiencing allergy symptoms when they are screened at clinics. It they say yes, they are asked to come back another day.
The individual whose blood donation seems to have triggered the boy's temporary food allergies has been asked not to give blood in future. But the blood agency does not routinely ask people with food or drug allergies to refrain from donating blood, nor is it considering doing so, Goldman said.
The reason? Such events are very rare, but donors with allergies are common. Losing them would jeopardize Canada's blood supply, she explained.
A survey the agency conducted around 2010 revealed that about 40 per cent of blood donors had some allergy and nearly eight per cent reported having severe allergies.
"To prevent less than one reaction a year — it's really quite a bit less than one a year — we would defer eight per cent of our donors (and that's) really very disproportionate," said Goldman, who noted that Hema-Quebec, which runs that province's blood supply, and the U.S. blood system take the same approach.
"The benefit-risk ratio is horrible on that one and we would jeopardize supply for very, very little increase in safety."