A hospital in New Hampshire has stopped giving type B and AB platelets to patients with type O blood because of a tick. New research published in JAMA Internal Medicine found that at US hospitals in regions where alpha-gal syndrome is common, type O patients who received B or AB platelets or plasma had nearly four times the risk of an allergic transfusion reaction compared with type O patients who received type O products.
The geographic qualifier is the finding. The same pattern did not appear at sites outside the United States, which points investigators toward alpha-gal rather than a general property of mismatched blood products.
For most people, this changes nothing about whether to accept a transfusion. For patients in the Lone Star tick's expanding range who need platelets or plasma, it may change which unit their hospital selects.
Chemistry That Connects a Tick Bite to a Blood Bag
Alpha-gal syndrome develops after certain tick bites, most often from the Lone Star tick in the United States, prompt the immune system to produce antibodies against galactose-alpha-1,3-galactose, a sugar found in most non-primate mammals but not in humans. People who become sensitized can have delayed, sometimes severe, reactions hours after eating beef, pork, lamb, or, in some cases, dairy and gelatin. The CDC's overview of the condition describes reactions ranging from hives and gastrointestinal symptoms to anaphylaxis.
The transfusion link rests on a structural resemblance. The B blood group antigen looks chemically similar to alpha-gal. Researchers hypothesized that antibodies primed by a tick bite might recognize the B antigen in a transfused product and trigger an allergic reaction in a recipient whose blood type is O.
Pathologists at Dartmouth Hitchcock Medical Center noticed the pattern first, seeing an uptick in recent years of severe and even life-threatening allergic reactions among type O patients who received platelets or plasma from B or AB donors. Richard Kaufman and Nancy Dunbar set out to test whether it held up beyond one hospital.
Numbers Behind the Association
The team analyzed 558,823 platelet and plasma transfusions at 40 hospitals in five countries, documenting 1,744 allergic transfusion reactions. They compared reaction rates by donor and recipient blood group, then grouped sites based on whether they were in regions with high or low alpha-gal prevalence.
At the nine US sites in high prevalence areas, significantly more allergic reactions occurred among type O recipients of B or AB units than among type O recipients of O units. The association was even stronger when researchers restricted the analysis to moderate and severe reactions in type O patients receiving type B products. The signal did not appear at non-US sites.
This is a retrospective cohort study, and its central limitation belongs at the front rather than the end. The researchers did not confirm alpha-gal allergy in every patient who reacted. What they established is an epidemiologic pattern consistent with the mechanism, not direct proof that alpha-gal antibodies caused each individual reaction. Patients may also have had other risk factors for allergic transfusion reactions that the analysis could not fully separate out.
The researchers have proposed the name transfusion-related alpha-gal syndrome, or TRAGS, and argue it should be treated as a legitimate manifestation of the condition rather than a curiosity.
One Hospital Has Already Changed Practice
Dartmouth Hitchcock is not waiting for confirmation.
Kaufman, the study's corresponding author and a professor of pathology and laboratory medicine at the Geisel School of Medicine at Dartmouth, said in a statement released by Dartmouth Health that he anticipates the work will "change transfusion practices in the U.S., at least in AGS high-prevalence regions." The medical center has already stopped giving B or AB platelets to type O patients.
Dunbar, the senior author, framed the result as part of a broader pattern of tick-borne illnesses arriving faster than clinical practice can adapt. "The changing climate and ensuing greater proliferation of ticks is leading to illnesses not previously seen, she said, adding that she hopes other hospitals in regions with high tick populations will follow and avoid B and AB units for type O patients needing platelets or plasma.
No national blood banking body has issued revised guidance. Whether the Association for the Advancement of Blood and Biotherapies or the FDA takes up the question is the next thing to watch, and any change would likely apply first to endemic regions rather than nationwide.
Practical Reading for Patients and Families
Nobody should decline a needed transfusion because of this study. Platelet and plasma transfusions treat bleeding, cancer, trauma, and surgical complications, and the risk of refusing one generally far exceeds the risk described here.
The useful action is disclosure. Anyone with a diagnosed alpha-gal allergy, or a history of unexplained reactions after eating red meat, should make sure it appears in their medical record and mention it before any planned procedure that might involve transfusion. Hospitals cannot select a different product if they do not know.
Risk is not evenly distributed. It concentrates among people with type O blood who live in or have spent time in areas where the Lone Star tick is established, primarily the southeastern, south-central, and mid-Atlantic United States, with the range expanding northward. It also occurs among patients who frequently receive platelets and plasma, including those undergoing cancer treatment or major surgery.
Anyone who experiences hives, flushing, wheezing, throat tightness, or a drop in blood pressure during or shortly after a transfusion should tell the nursing staff immediately. Reactions during a transfusion are managed on the spot, and staff are trained to stop the infusion and treat symptoms.
MedicalDaily previously reported that many people carry alpha-gal antibodies without ever developing the allergy, a distinction that matters here too. A positive antibody test alone does not establish that someone has alpha-gal syndrome, and clinicians have warned against overdiagnosis based on serology without compatible symptoms.
The researchers say further work is needed to pin down the mechanism and identify the most effective precautions. Additional hospitals in endemic regions may adopt changes to product selection before any formal guidance is issued.
Key Questions Answered
What did the study find? Among type O patients at US hospitals in regions where alpha-gal syndrome is common, receiving B or AB platelets or plasma was associated with nearly four times the risk of an allergic transfusion reaction compared with receiving type O products. The pattern did not appear at sites outside the United States.
How large was the study? Researchers analyzed 558,823 platelet and plasma transfusions across 40 hospitals in five countries and documented 1,744 allergic transfusion reactions. It was published in JAMA Internal Medicine.
Does this prove alpha-gal caused the reactions? No. This is a retrospective cohort study. It provides epidemiologic evidence consistent with the proposed mechanism, but researchers did not confirm alpha-gal allergy in every patient who reacted.
Should anyone refuse a transfusion because of this? No. Transfusions are life-saving treatments, and the risk of declining a needed one is generally far greater. The practical step is to tell the care team about any alpha-gal diagnosis or a history of red meat reactions.
Who is most affected? People with type O blood who live in or have visited areas where the Lone Star tick is established, particularly patients who receive platelets or plasma often, such as those undergoing cancer treatment or major surgery.
Has any hospital changed what it does? Yes. Dartmouth Hitchcock Medical Center has stopped giving B or AB platelets to type O patients. No national blood banking body has issued revised guidance.
What symptoms signal a transfusion reaction? Hives, flushing, wheezing, throat tightness, or a drop in blood pressure during or shortly after a transfusion. Tell nursing staff immediately so the infusion can be stopped and symptoms treated.
