In emergency situations, patients are given universal blood transfusions until their blood type is identified. However, this greatly decreases the supply of universal blood for individuals with rare blood types. A new study published in The Lancet Hematology assessed the risks of having a transfusion reaction after receiving an incompatible blood type.


When a red blood cell (RBC) transfusion is to occur, there are two important blood group systems that clinicians must consider. The first is the ABO blood group system which is based on the presence or absence of two antigens on the surface of RBCs. Individuals with type A blood have the A antigen on their RBCs and B antibody in their plasma. The opposite is true for individuals with type B blood. Therefore, an individual with type A blood cannot receive type B blood, as their type B antibodies will recognize the type B antigen in the blood and attack the transfused RBCs. Individuals with AB blood have both A and B antigens and can receive either type of blood. Lastly, individuals with type O blood have neither type A nor B antigens but have both antibodies; thus, they can only receive type O blood, but can donate to any other blood group.

In addition to A and B antigens, there is a third antigen called the Rh factor. Individuals either have Rh factor (Rh+) or do not (Rh-). Individuals who are Rh+ can receive either type of blood, while those who are Rh- can only receive other Rh- blood. Taken together, individuals with blood group O Rh- are true universal donors because their RBCs will not induce hemolytic transfusion reactions due to incompatibility in anyone.

In emergency situations when patients are experiencing substantial bleeding, they are typically transfused with type O Rh- blood until their blood group has been determined. However, only 6-8% of the blood donor population have the blood group O Rh-. Additionally, approximately 85% of individuals are Rh+. Therefore, the universal use of O Rh- blood in emergency situations leads to a very high consumption of O Rh- blood and consequently increases the risk of blood shortages.

Importantly, if an Rh-patient is transfused with Rh+ blood, there is the risk for the formation of anti-D antibody against Rh+ between 3-12 weeks following transfusion. This is particularly concerning in girls and women of childbearing age as immunization against Rh+ can result in severe hemolytic disease in the fetus during subsequent pregnancies. In some major trauma centers, type O Rh+ blood is given to males in emergency situations. In addition, during Rh- blood shortages, Rh+ blood must be given to patients.

A new study published in The Lancet Haemotology conducted a single-center observational study between 2001 and 2015. In this study, researchers assessed emergency room patients who were Rh- and received Rh+ blood during transfusions, either due to unknown status or shortages in type O Rh- blood. These patients were followed up with for up to 12 months to assess anti-D alloantibody formation.

Out of 437 emergency-room patients with initially-unknown blood types, 85 (20%) were Rh- and received a transfusion with Rh+ blood. The study found that the overall risk of inducing anti-D antibodies in all patients regardless of Rh status was 4%. Strikingly, an additional 110 known Rh-  patients received Rh+ blood transfusions during type O Rh- blood shortages. From this group of patients, 26% developed anti-D immunization.

This study had two major findings. First, transfusion emergency patients with an unknown blood type receiving Rh+ blood transfusions had a low risk of inducing anti-D antibodies, but doing so saves more than 10% of total type O Rh- blood for those who require it. This is likely because only 15-20% of the population is Rh- so the risk of developing anti-D immunization are lower for the overall population. However, for patients who were known Rh- and received Rh+ blood, 26% had a hemolytic transfusion response and developed anti-D antibodies. This demonstrates the great need to establish better methods to conserve Rh- blood for individuals who need it.

Possible strategies include only giving Rh- blood to individuals of unknown blood type if they are women of child-bearing age or younger, as there are major risks associated with anti-D antibody development for women during future pregnancies. Additionally, programs can be implemented to test individuals for their blood types and have this information accessible on a health card or other form of identification. This could greatly decrease the overconsumption of type O Rh-blood and ensure individuals are receiving the correct type of blood in emergencies.


Written By: Neeti Vashi, BSc

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