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Risks of Transfusing Unmatched Red Blood Cells

We often "get away" with transfusing unmatched Red Blood Cells because the incidence of unexpected antibodies in patients experiencing medical emergencies is thought to be relatively low ( ~3-5% is sometimes cited, but with little solid evidence).

Antibody incidence may vary according to several factors:

  • Genetic disposition
  • Patient's underlying disease
  • Number of prior transfusions
  • Gender (females may get exposed to foreign antigens via fetomaternal bleeds as well as transfusion)
  • Concordance of antigen phenotypes of patients vs blood donors in a given locale.
In general, antibody incidence increases with the number of transfusions that are given, although most antibody producers will respond within the first 3 - 4 transfusions. Antibody incidence in transfusion-dependent patients, such as those with sickle cell anemia or thalassemia, is very high.

Regardless of likelihood, transfusing uncrossmatched blood to a patient with unexpected antibodies can result in a serious hemolytic transfusion reaction.