Rhesus system | Blood groups

Rhesus system

Just like the AB0 system of blood groups, the Rhesus system is one of the most important blood group systems today. These are antibodies against blood components. The name comes from experiments with rhesus monkeys, through which the rhesus factor was discovered in 1937 by Karl Landsteiner.

Due to the already existing A and B blood group nomenclature for the previously discovered AB0 system, he continued to use this as C, D and E. The rhesus factor D is particularly important. It can be present in a human being, i.e. positive (D+), or non-existent and therefore negative (d-). The rhesus factor is inherited dominantly, which is why the rhesus negative blood group is rare.

Function of the rhesus systemThe antibodies against the rhesus factor are only formed after contact with it, for example during pregnancy or blood transfusions. Thus, in rhesus-negative mothers it can lead to complications of the blood groups in a second pregnancy. It is not the mothers but the fetuses that are at risk.

Through contact between the fetal Rhesus-positive blood of a fetus and the Rhesus-negative blood of the mother, the latter forms antibodies against the Rhesus factor. The mother herself does not have any problems with this, as she does not have the corresponding antigens. If, however, a new pregnancy with a rhesus-positive child occurs, the antibodies formed by the mother can destroy the erythrocytes of the fetus and thus lead to hemolyticus neonatorum disease or even death.

This complication can be counteracted by blood exchange. However, this is no longer necessary nowadays, as anti-D prophylaxis is already carried out during the first pregnancy, which prevents antibody formation. The Kell system is the third most important blood group system.

In case of incompatibility between donor and recipient this also leads to a hemolytic transfusion syndrome and can be fatal. For this reason, all blood donors in Germany and Austria are usually tested for the Kell antibody. Approximately 92% of the population are Kell negative, about 7.2% are heterozygous and can receive Kell negative or positive blood.

Only about 0.2% of the population are Kell positive and need Kell positive blood for blood transfusions. For this reason, Kell negative blood can be used for transfusions in almost every patient. The Kell system is based on 34 known antigens encoded by genes of chromosome 7.

The Kell system also plays an important role in pregnancy and, similar to the Rhesus system, can lead to the formation of antibodies by the mother and thus to risks in a second pregnancy. However, Kell incompatibility occurs much less frequently than Rhesus incompatibility. Nevertheless, it is tested during pregnancy, in addition to the other blood group determinations. However, there is no prophylaxis as there is for Rhesus incompatibility. For this reason, close monitoring of the pregnancy is indicated.