What is the function of a blood group

Blood types

The AB0 system

The Austrian immunologist Karl Landsteiner presented the AB0 blood group system in 1901. While studying immune responses, Landsteiner discovered two different antigens, which he named A and B, on the surface of red blood cells. Antigens are substances that cause the formation of antibodies as soon as they are recognized by the organism.

After Landsteiner found out that not everyone has the same antigens on red blood cells, he was able to name the four classic blood groups A, B, AB and 0.

A person with blood group A has antigen A on the surface of his red blood cells, while antigen B is present in group B accordingly. Blood group AB means that the red blood cells have both antigens. After all, people with blood group 0 have neither the A nor the B antigen.

According to the missing antigens, the immune system creates so-called antibodies. This means that a person with blood group A has antibodies against B and vice versa. In contrast, no antibodies are formed with blood group AB, while group 0 means that both antibodies against A and against B are present.

For example, if group A blood is mixed with group B, the antibodies against the foreign antigens become active. If this happens during a blood transfusion, life-threatening complications can occur. This is because the red blood cells clump together.

Therefore, the success of transfusions before the introduction of the AB0 system was rather accidental. Karl Landsteiner received the Nobel Prize for Medicine in 1930 for his discovery.

The rhesus system

The second important system for determining blood groups is also a result of Landsteiner's research. Together with the American hematologist Alexander S. Wiener, he discovered the so-called Rhesus system in 1940, named after the monkeys of the same name that were used as experimental animals.

Wiener and Landsteiner found that the rhesus factor was another antigen on the red blood cells. People who have this antigen are said to be rhesus positive, whereas blood without this factor is rhesus negative. Analogous to the AB0 system, rhesus-negative people develop antibodies against rhesus-positive blood. So this factor must also be taken into account with blood transfusions.

The Rh factor is also very important in pregnancy. If the father is rhesus positive but the mother is rhesus negative, the child will also be positive. During childbirth, blood from the fetus can penetrate the mother's circulation and trigger the immune reaction described above. When the first child is born, this is not a major problem, as the antibodies have to be formed first.

With every further pregnancy, however, the risk of a life-threatening defense reaction increases because the antibodies are already present. Today, however, so-called anti-D prophylaxis is usually carried out during the first pregnancy in order to suppress the mother's antibody production.

Distribution of blood groups

Not all blood groups are equally common. The medical lexicon "Pschyrembel" gives the following distribution for Central Europe: Group A: 44.5 percent, B: 10.5 percent. AB: 4.5 percent. 0: 40 percent.

The different forms of the Rh system are by no means balanced. About 85 percent of the European population are rhesus positive, which is why there is a constant shortage of rhesus negative donor blood.

The distribution of blood groups also differs considerably depending on the continent. For example, blood group 0 occurs in over 90 percent of the native Americans, while group B dominates in Asia.

People with blood group 0 are considered universal donors. Their blood can be received by all other groups. Universal recipients are accordingly people from group AB, since blood from groups A, B and 0 can also be transferred to them in an emergency. In both cases, however, blood from the same group is generally preferable as a donation.