American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Type O blood is defined as being the universal donor due to the absence of A and B antigens on the surface of the red blood cells. This characteristic means that individuals with Type O blood can donate blood to people of any blood type without the risk of their immune system rejecting the transfusion based on the presence of incompatible antigens.

While Type O blood does contain anti-A and anti-B antibodies in the plasma, these antibodies are not an issue during the donation process because the donated red blood cells will not have either A or B antigens. Thus, Type O blood can be given to recipients of any blood type without causing an immunological reaction.

This is in contrast to other blood types, which have specific antigens that can cause transfusion reactions if given to incompatible recipients. Consequently, the defining characteristics of Type O blood make it invaluable in emergency situations where blood compatibility is crucial.