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Blood types: A, B, AB, 0, positive and negative

The structure of red blood cells determines the blood type. The most important blood group properties for blood transfusions are the AB0 and Rhesus system

 

he most important thing to blood groups:

The AB0 blood group is an individual characteristic of the red blood cells. The red blood cells may in their membrane containing antigens A and / or B, or they contain no antigens (blood group 0). The blood group can, however, also on blood serum recognize, because each blood type is characterized by certain antibodies that are free in the blood swim. Each blood type contains only antibodies against foreign blood groups. Example: Blood type A (antigens "A" on the red blood cells) contains only antibodies against type B blood (anti-B). When blood transfusions, it is important that donors and recipient have the same blood group - otherwise the blood would clump together.

What's "blood"?



The red blood cells ( erythrocytes ) are ring-shaped cells that carry oxygen and carbon dioxide through the bloodstream. The "shell" of red blood cells is called "membrane". In this membrane stuck many different proteins. These proteins, which impart the red blood cells in a specific surface structure are called "antigens". The "blood group proteins" A and B are also those antigens.

For the AB0 blood group, a distinction the A, B, AB and 0 (zero) property. People with blood type "0" have none of these blood group antigens on the surface of their red blood cells. People with blood type "AB" both proteins (A and B) are included in the erythrocyte membrane. In blood group "A" is only the antigen "A" exists in the blood group "B" only the antigen "B".

What are blood group antibodies?



The blood is not only the red blood cells, but also alone on blood serum, ie at the blood plasma without red blood cells recognize. Because the blood swim inherently specific proteins, so-called "blood group antibodies". They are constructed Y-shaped and can be combined with matching antigens. Thus, the own blood clots not antigen-antibody compounds, the blood contains no antibodies against their own blood type, but antibodies against foreign blood groups.

That means:
  • When blood type "A" blood contains antibodies against the blood group "B" (anti-B).
  • The blood group "B" is characterized by antibodies against the blood group "A" of (anti-A).
  • People with blood type "0" in their blood both antibodies against blood group A and blood group B against (anti-A antibodies and anti-B antibodies).
  • When blood type "AB" no antibodies to blood group A or B are present.
The blood group antibodies are among the so-called "immunoglobulin M (IgM)". They are a lifetime in the blood. In pregnant women it can not cross the placenta. Therefore, it is not harmful if the baby in the womb has a different AB0 blood group Herself. (However, different "Rhesus properties" cause problems, see below.)

How is the AB0 blood group inherited?

The blood type is inherited from parents to their children. Each child will receive a blood group characteristic from the father and one from the mother. In fact, can be further divided the blood groups. Blood type "A" means that the person's blood type "A0" (heterozygous) or "AA" ("homozygous") may have. The blood group "B" can be shown as "B0" or "BB". The blood type "0", however, is always "homozygous", or "00". The antigens "A" and "B" are dominant - they always prevail. The blood type "AB" is called "heterozygous".

What happens when a blood transfusion? What is a "bedside test"?

When a patient's blood from another person receives ( blood transfusion ), in addition the physician is testing just before the transfusion, if the patient's blood (recipient) really compatible with the donor's blood. A patient can only tolerate the blood of a donor who has a matching blood type to him. Otherwise risk of serious diseases and even death. The so-called "bedside test", ie the test directly at the bedside to ensure that the donor and recipient blood match.

What's Rhesus system? What is the "plus" or "minus" after the blood type designation?

In addition to blood group system "AB0" There is more, including the "Rhesus system". The erythrocytes Rhesus positive people carry on their surface a "D antigen" (Rhesus factor "D"). Rhesus-negative people do not have this antigen. Physicians characterize a rhesus positive blood group with "+" and a rhesus negative blood group with "-". For example, the term "blood group 0+" that it is "positive blood group 0, Rh factor" to the concerns.

What is the role of the Rhesus factor in pregnancy?



Unlike the AB0 system the blood of rhesus negative people usually does not contain antibodies to the Rhesus feature D. This "D antibodies" but can develop in rhesus negative people - namely when the rhesus negative blood with rhesus positive blood comes into contact. This mechanism can play an important role in pregnant women.

Normally, the blood circulations of mother and child during pregnancy are separated. If medical procedures or in the birth of the child's blood may come into contact with the mother's blood. If a Rhesus-negative pregnant women discharged a Rhesus-positive child, then performs a contact with the blood of the child means that the antibodies against the blood of pregnant rhesus positive child produces. This happens relatively slowly and usually does not lead in a first pregnancy problems. If Rhesus-negative mother but again pregnant with a rhesus positive child, then performs a renewed contact with blood very quickly to the formation of antibodies in the mother. Because the mother is "aware" of the first child, which means that their immune system has formed memory cells. Since the D-antibody immunoglobulin type G (IgG immunoglobulins), they can easily pass through the placenta into the blood of the child. There, the D antibodies destroy the mother's blood of the child. This may at worst cause birth defects or death of the child.

Rhesus prophylaxis during pregnancy



Thus the above-described case does not occur every rhesus negative mother is in the 28th to 30th week of pregnancy a "Rhesus prophylaxis". The woman doctor injects a small amount of nut D antibodies into the blood. This amount is so small that it does not endanger the child. The mother's body receives the information, however: "There are already D antibodies present." Hence, the mother forms of itself no other D antibodies. A "sensitization" thus remains out. The D prophylaxis is repeated within 72 hours after birth.

The reverse, ie a Rhesus positive mother carries out a Rhesus-negative child, does not cause any problems - neither the child nor with the mother.

The transfusion Rhesus positive blood to a Rhesus-negative patients can result in the formation of D antibodies. Therefore, they should be avoided in women of childbearing potential unless she is no alternative and vital.

What blood type are frequently?



37 percent of people in Germany have the blood group "A +". About 35 percent carry the blood group "0+". The blood group "B +" is at 9 percent of people in Germany, the blood group "O" and "0-" at 6 percent each. Finally, there are the blood types "AB +" with 4 percent, "B-" with 2 percent and "AB" with 1 percent.




Important: The reference values ​​and the measured values ​​can differ greatly from one laboratory to another. Furthermore, there may be strong diurnal and (seasonal) seasonal variations without disease value. Before you can be confused by different results, therefore, ask your doctor to tell you your personal data. Individual laboratory values ​​alone are also mostly inconclusive. They often need to be assessed in the context of other values ​​and over time.


Technically checked by Prof. Dr. med. Michael Spannagl , Laboratory of Immunogenetics and Molecular Diagnostics, Hospital of the Ludwig-Maximilians-Universität (LMU) München