The incidence rate is so low that it’s hardly worth worrying about.
Yet, for those few who have their first food reaction after receiving a blood transfusion the consequences can be life-threatening.
Case In Point
An eight-year old Canadian boy, for instance, with no history of food allergy received a blood transfusion for a medical condition. Weeks later, as reported in the Canadian Medical Association Journal (CMAJ), he experienced anaphylaxis shortly after eating salmon.
Four days after the salmon reaction, this boy needed emergency care again after ingesting a peanut butter cup. A subsequent inquiry found the boy’s blood donor* was indeed allergic to fish, shellfish, and peanuts.
“It’s very rare to have an allergic reaction to a previously tolerated food,” said the CMAJ report’s senior author, Dr. Julia Upton. “The overall idea is that he wasn’t allergic to these foods,” until transfusion acquired IgE (immunoglobulin E) antibodies triggered a reaction to them.
Temporary and Rare
Fortunately, allergies acquired via donated blood are expected to be temporary. Since the Canadian boy’s body did not manufacture the IgE antibodies responsible for his food reactions, the acquired allergies resolved within a few months.
Along with the blessing of temporariness, allergy transfer by transfusion is also rare. There are three reasons for this:
- The donor’s blood must contain a high level of specific IgE antibodies that react to food allergens.
- A substantial amount of the transfusion product must be given to the recipient.
- The recipient must then ingest the specific food transmitted antibodies react to – within the tight time frame of a few months – since passively acquired antibodies eventually fade from a recipient’s bloodstream.
Because the improbable confluence of these three circumstances makes transfusion-acquired allergy unlikely, individuals with allergies are not barred from donating blood in the U.S. or Canada.
Though it would be reassuring to know the possibility of allergy-by-transfusion was being preempted, doctors and researchers are unclear how to accomplish this. Testing donated blood for IgE antibodies is impractical since many people with high levels do not have allergies, while others with low IgE levels do.
“Clearly, the safety of the [blood] supply is of everyone’s utmost concern,” says Upton, but further research is necessary to learn how often allergy transfer happens, and how best to prevent it.