Universal donor: what is it?

A universal donor is someone who can give their blood to everybody. This is an individual from blood group O and rhesus negative. In France, only 6% of the population are universal donors according to theFrench blood establishment. But 36% would be group O+, which allows them to donate their blood to groups O+, A+, B+ and AB+, i.e. around 85% of the population. In contrast, the universal receiving group is AB+. For plasma donation, people with group AB are universal donors.

The Red cells people with group O have neither A antigen nor B antigen. If a blood donor is for example group A, his red blood cells carry A antigens and will be recognized as foreign in recipients of group B or O, who have antibody anti-A: the blood cells of the donor would be destroyed by the immune system of the recipient by hemolysis and the transfusion would then be a failure. Hemolysis can have serious consequences on the recipient.

ABO system and rhesus system

The ABO blood group system was discovered in 1900 by Karl Landsteiner, Nobel Prize for Medicine in 1930. He observed the agglutination of red blood cells in the presence of human serum. He had deduced the existence of two antigens called A and B on red blood cells. In fact, the ABO system corresponds to the presence on the membrane of red blood cells of polysaccharides ; those sugars depend on the presence of certain enzymes.

The rhesus system is based on the presence (rhesus positive) or absence (rhesus negative) of the D antigen on the red blood cells. Its name comes from the monkey rhesus macaque in whom this blood group system has been described.