How do we preserve universal blood for those that need it most?

by Dr. Frances Compton

We are all taught that type O Rh negative (O-) red blood cells (RBCs) are the universal blood product for transfusion. But how does this practice affect our overall blood supply? The emergency use of O- blood for all patients may actually deplete that limited resource for those that need it most.

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Since D- patients do not inherently make anti-D antibodies (unlike ABO), D+ RBCs are not inherently incompatible with D- patients. This is contrary to type A or B RBCs which must never be given to type O patients - because anti-A and anti-B antibodies are naturally occurring. In contrast, D- patients must be exposed to the D antigen (either through blood transfusion or pregnancy) in order to become alloimmunized and make an anti-D antibody. 

If this is the case, then why do we care so much about the D antigen? It’s even part of a patient’s blood type – the ABO AND Rh status make up a patient’s blood type that we routinely match for! Well, the D antigen is the most immunogenic of all of the other (non-ABO) RBC antigens that result in clinically significant antibodies. D- patients become alloimmunized at a rate of ~20% after exposure to the D antigen. This is most impactful for one population in particular; young female patients with the potential to become pregnant. The anti-D antibody is an IgG antibody which can be potentially harmful to D+ babies born to D- mothers. This condition is called hemolytic disease of the fetus and newborn and it is the main reason we try to match RBCs for the D antigen.

So, going back to the use of O- blood as the universal blood type - while this is technically true, it does not impact all patients the same way. For D- women >55 years and all men, the potential formation of an anti-D antibody is of minimal clinical impact to them. As long as they have not already formed an anti-D antibody, then they can safely be transfused D+ RBCs. In the event that they do form an anti-D antibody, they will simply require D- transfusions in the future. This highlights the importance of preserving our already limited supply of O- blood for the patients who need it most; D- women with childbearing potential.

In emergency situations and during times of low blood supply, it is best to plan for the worst-case scenario. If O- RBCs are in low supply, plan ahead and switch to O+ transfusions for all patients who will be least affected. Adult men and women without childbearing potential will have little impact to their future health even in the unlikely chance that they form an anti-D alloantibody.

References:

Callum JL, Waters JH, Shaz BH, et al. The AABB recommendations for the Choosing Wisely campaign of the American Board of Internal Medicine. Transfusion 2014; 54: 2344-52.

AABB Choosing Wisely list: https://www.choosingwisely.org/societies/american-association-of-blood-banks/ Released April 24, 2014, Accessed April 22, 2021.

 AABB Technical Manual, 19th ed. 2017. Edited by Fung M, Eder AF, Spitalnik SL and Westhoff CM.