An ABO mismatch during transfusion can be lethal.  Blood transfusion should be considered a form of organ transplantation – administering an ABO incompatible RBC transfusion can result in massive hemolysis, renal failure, respiratory failure and death.  Due to this, LTOWB transfusion is always the safest option if the recipient’s blood type is unknown.  Type O blood is the universal donor because the red blood cells (RBCs) do not express the A and B antigens to which the recipient might have naturally occurring hemolytic antibodies. While this CPG is not meant to make everyone a transfusion expert – understanding the basics on blood types and titers will help to ensure that this life-saving capability (blood transfusion) is implemented safely. 

Figure 2. Comparison of blood types

Type O Blood – comprises approximately 45% of the US population.  Type O RBCs do not express A and B antigens, which is what makes it the ‘Universal Donor’ type.  Type O blood contains both anti-A and anti-B antibodies in the plasma. Type O patients can only receive Type O WB or LTOWB.

Type A Blood – comprises 40% of the US population.  Type A individuals express the A antigen on the RBCs and anti-B antibodies in the plasma.  Type A patients can receive Type A WB or LTOWB.

Type B Blood – comprises 10% of the US population.  Type B individuals express the B antigen on the RBC and anti-A antibodies in the plasma. Type B patients can receive Type B WB or LTOWB.

Type AB Blood – comprises just 5% of the US population.  Type AB RBCs express both Type A and Type B antigens and therefore do not have circulating anti-A or anti-B antibodies in their plasma. This makes Type AB the ‘Universal Recipient’ for RBCs and the universal donor for plasma because their plasma does not contain anti-A or anti-B.  Type AB patients can receive Type AB WB or LTOWB.