Blood groups

Blood can be divided into groups based on various characteristics. Today there are about 30 known blood group systems. For everyday medical use many of them are insignificant, but for certain diseases they can be important. The best known blood group systems are the AB0 and the Rhesus system.

Karl Landsteiner: discoverer of blood group systems

The Austrian physician Karl Landsteiner discovered at the beginning of the 20. The AB0 blood group system of the twentieth century. Together with the American Alexander Salomon Wiener, he also discovered the rhesus system in 1937.

The AB0 blood group system

All red blood cells (erythrocytes) are surrounded by a sheath. There are characteristic structures (antigens) on this envelope that distinguish the red blood cells of one person from those of another.
In the AB0 blood group system, the antigens on the envelope of red blood cells are divided into four groups: A, B, AB and 0 represent the four blood groups.

  • Blood Type A: There is only antigen A on the envelope of red blood cells.
  • Blood group B: only antigen B is present.
  • Blood group 0: No antigens are present.
  • Blood group AB: both antigens A and B are present on the red blood cells.

The blood groups can be distinguished not only by the red blood cells. In the blood plasma there are special proteins: the blood group antibodies. These antibodies are able to recognize blood of a foreign blood type.


For example, a person with blood group A has antigens A on the red blood cells and antibodies B in the blood plasma. With the blood group B it behaves exactly the other way around. Blood group 0 has antibodies A and B and blood group AB has no antibodies at all in the blood plasma.

The rhesus system of blood groups

In the Rh system there is blood with the "Rh factor positive (Rh+)" and blood with the "Rh factor negative (Rh-)". If someone is rhesus positive, it means that the rhesus antigen is present on the red blood cells. In rhesus-negative people the antigen is missing.
By the way, these antigens were first researched in rhesus monkeys, hence the name.

Blood groups must be compatible for blood transfusions

For blood transfusions, the AB0 and Rhesus blood group systems are of particular importance, as it can be dangerous if donor and recipient blood groups do not match. Because: Blood cannot be transferred arbitrarily from one person to another. The blood groups must be compatible. If one were to transfer the blood of another person indiscriminately, there would be the danger of a serious defense reaction against the donor blood: The antibodies in the blood recognize the "wrong blood" and combine with the antigens on the red blood cells (erythrocytes), which leads to dangerous blood clots. To prevent this from happening, donor and recipient blood must be compatible.

Distribution of blood groups

The blood groups are distributed very differently from region to region. In Central Europe and Germany, blood groups A and 0 are most common. Rarer are blood groups B and AB. Most people have rhesus-positive blood.

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