Blood groups: what are they and what distinguishes them?

Blood group 0, AB, A or B? Many people do not know what blood type they have. Most of the time this is not necessary. Only when a blood transfusion is due or a  pregnancy  occurs does the knowledge of the blood group become more important and can become essential for (survival) life. What the individual blood groups are all about, how common or rare each blood group is, how blood groups are determined, which blood groups go together and much more interesting information about blood and blood groups can be found below.

Blood types – what makes the difference?

The classification of blood into individual blood groups depends on whether certain characteristics are present or not. These characteristics are the proteins found on the surface of the  red blood cells  (erythrocytes) , which are also known as  blood group antigens  .

The two most important systems used in medicine to classify antigens and determine blood groups are:

  1. The AB0 blood group system
  2. The Rhesus blood group system

The type of antigen and their – possibly simultaneous – occurrence on the surface of the red blood cells determines the blood group affiliation.

In addition, various antibodies are present in the blood. These are proteins that belong to the  immune system  and are designed to recognize and bind to antigens, such as foreign substances or pathogens. People with a certain blood group also have antibodies against foreign blood groups or antigens, the so-called  blood group antibodies.

A person never has antibodies against their own blood group antigens in their blood, because the consequences could be fatal: the binding of antibodies and antigen would trigger an immune reaction that would cause the blood cells to clump together dangerously. This would stop the transport of oxygen and carbon dioxide and cellular respiration, which could result in death.

What blood groups are there?

Blood grouping plays a crucial role in blood transfusions. Because the blood of the donor and recipient must match each other – it is also said that it must be compatible – so that there is no undesired reaction of the immune system and the blood does not clot.

Blood groups A, B, AB and 0

According to the  AB0 blood group system  , there are blood groups A, B, AB and 0:

  • Blood group A: Only the antigen A is found on the surface of the red blood cells.
  • Blood group B: Only the antigen B is present.
  • Blood group AB: Both antigens A and B are found on the red blood cells.
  • Blood group 0: Neither antigen A nor B is present.

At the same time, the blood group antibodies A and B found in the blood plasma can also be assigned to the individual blood groups:

  • Blood group A: Antibody B
  • Blood group B: Antibody A
  • Blood group AB: no antibodies
  • Blood group 0: antibodies A and B

If you summarize the affiliation of antigens and antibodies for each blood group in a table, then it becomes clear that there are never antibodies in the blood plasma that also match the antigens on the surface of your own red blood cells.

blood type antigen (red blood cells) antibodies (blood plasma)
AB A and B
0 A and B

Rhesus factor positive or negative

Another system that complements the determination of blood groups and is of great importance for blood transfusions is the  Rhesus blood group system.

In the Rhesus blood group system, a distinction is made as to whether one of the so-called Rhesus factors occurs on the red blood cells. This is a large group of blood group antigens, which includes a total of 55 different antigens. The most important of these is the Rhesus factor D, which is also the basis for the classification of the Rhesus blood group system. If this antigen is present, then one speaks of “Rhesus factor positive” (Rh+), if it is missing, then the blood group is called “Rhesus factor negative” (Rh-).

How many blood groups are there?

A total of eight blood groups can be distinguished on the basis of the systems mentioned above and through the respective combinations of the individual characteristics   :

  • Blood group A Rh+ (A positive)
  • Blood group A Rh- (A negative)
  • Blood group B Rh+ (B positive)
  • Blood group B Rh- (B negative)
  • Blood group 0 Rh+ (0 positive)
  • Blood group 0 Rh- (0 negative)
  • Blood group AB Rh+ (AB positive)
  • Blood type AB Rh- (AB negative)

So what does it mean when a person has blood type 0 positive?

  1. Antigens A and B are absent from the surface of red blood cells.
  2. Antibodies A and B are present in the blood plasma.
  3. Rhesus factor is present on the surface of red blood cells.

Which blood groups match?

One cannot say in general that only the same blood groups fit together and are suitable for a blood transfusion. Tolerability also depends on whether it is donor or recipient blood.

For example,  blood group 0 is the perfect donor blood  because the red blood cells do not have antigens that can trigger an immune reaction in blood group A, B or AB recipients. Conversely, blood type  AB is the best blood type for a recipient.  Because there are no antibodies in the blood serum of recipients with blood group AB and they can therefore receive all other blood groups without an immune reaction taking place.

The following table provides an overview of which blood types match, depending on who is the donor or recipient:

Spender*in: 0 Spender*in: A Spender*in: B Spender*in: AB
Recipient: 0 gets along does not get along does not get along does not get along
Recipient: A gets along gets along does not get along does not get along
Recipient: B gets along does not get along gets along does not get along
Recipient: AB gets along gets along gets along gets along

The Rhesus factor also plays a role in blood group compatibility. People who are rhesus positive can get both rhesus positive and negative blood. Conversely, if you are Rhesus negative yourself, you can only receive blood that is also negative. Therefore,  Rhesus factor-negative blood is  particularly in  demand for blood donations.

How important is the Rhesus factor in pregnancy?

If a Rhesus-negative woman is expecting a Rhesus-positive child, a so-called Rhesus intolerance can occur, especially when the second child is born. This occurs when small amounts of the child’s blood enter the mother’s bloodstream during the first pregnancy.

The result: the mother’s body evaluates the child’s blood as foreign and forms antibodies against the child’s Rh-positive red blood cells. If you get pregnant again with a Rhesus-positive child, there will be a lot of antibodies against the Rhesus factor right from the start. These can reach the child via the placenta and destroy the child’s red blood cells there.

However, there are now tests that can be used to determine the blood group of the unborn child. If there is a risk of rhesus intolerance, the doctor treating you will initiate appropriate treatment to prevent possible complications.

How common are the blood types?

The distribution of each blood group varies by region. In Germany, blood group AB is the rarest blood group. It only occurs in 5 percent of people in this country. The most common blood types are A and 0. 85 percent of people are Rhesus positive and 15 percent are Rh negative. Taking the Rhesus factor into account, the following percentage frequencies result for the population in Germany:

blood type rhesus factor frequency
0 + 35 %
6 %
A + 37 %
6 %
B + 9 %
2 %
AB + 4 %
1 %

What is the rarest blood group in the world?

As mentioned above, in the Rhesus blood group system there are a total of 55 different antigens on the surface of red blood cells. If the red blood cells lack all of these antigens, then one also speaks of  “golden blood”.  This blood represents the rarest blood group in the world. Only 43 people worldwide are known to have this rarity in their veins.

How does blood group inheritance work?

Mendel’s laws describe how the inheritance of blood groups works. For each antigen, i.e. the characteristic of a blood group, humans have a gene that consists of two variants. These variants are also called alleles. Here’s how inheritance works:

  • Depending on the combination of alleles A and B, antigens A or B are formed on the surface of the red blood cells. Allele 0 does not produce antigens.
  • Each parent inherits only one allele to the child. So there is a combination of one allele from the mother and one from the father.
  • It is important to know that the alleles A and B are inherited dominantly over 0. So if A is combined with 0, then A “wins” and the antigen A is formed, blood group A is formed.
  • On the other hand, A and B are equivalent and both antigens are formed. Blood group AB is the result.
  • There can be differences in blood groups depending on whether the same allele was inherited from both parents or whether different alleles are present. For example, blood group A can mean that you have the alleles AA or A0. Blood group 0, on the other hand, always means that you have the allele 00, because in combination with another allele this would have prevailed dominantly. If both parents have the A0 allele, the child can therefore have blood type A (with the alleles AA or A0) or blood type 0 (alleles 00).

Chance decides which of the two alleles is passed on to a child by the father and mother. This can result in the following blood groups shown in the table:

combination of alleles from the parents Possible blood group of the child
A + 0 A or 0
A + A A or 0
B + 0 B or 0
B + B B or 0
A + B A or B or AB or 0
0 + 0 0
0 + AB a or B
A + AB A or B or AB
B + AB A or B or AB
AB + AB A or B or AB

How to determine the blood group?

If you want to have your blood group determined, you have a number of options:

  1. The easiest way is to have your family doctor determine your blood group. If you are interested, speak to them about a blood group test at their next visit. The only disadvantage: the health insurance company does not cover the costs for the test, so you have to bear it yourself.
  2. With a blood donation, the blood group determination is included and completely free of charge. So if you want to do something good, donate blood and you will automatically find out what blood group you have.
  3. Rapid tests for determining the blood group are available in the pharmacy or in the online shop. This way you can find out your blood type yourself in the comfort of your own home. Carrying out such a test is very simple, detailed instructions are usually included.
  4. At the beginning of pregnancy, the mother’s blood group is determined as part of the normal check-up. This is important because there can be incompatibilities between the mother’s and the child’s blood, which must be recognized in advance in order to avoid complications. The decisive factor here is the determination of the Rhesus factor.

Does blood type have an impact on COVID-19?

While some people do not notice their infection with the  corona virus  , others have to be artificially ventilated for a long time.  It is still not clear why  COVID-19 progresses so differently in people. In addition to numerous other factors, blood groups are also suspected, as a study from Denmark shows. In this study it was found that people with blood group 0 are less likely to contract COVID-19 than those with blood group A, B or AB.

According to a study from Canada, there is additional evidence that the severity of the disease also depends on the blood group. According to a German-Norwegian study, blood group A in particular could favor severe courses. However, further studies are needed to examine these relationships more closely and to confirm the initial results.

What is a blood group diet?

The so-called blood group diet (blood group nutrition) was developed by the American naturopathic researcher Peter D’Adamo in 1996. According to this diet, certain  foods are  assigned to the individual blood group types, which are supposed to be particularly healthy for these groups and help with weight loss.

There is no scientific evidence of any health benefits or the effectiveness of this diet. This is the result of an analysis of existing studies on this subject by the Belgian Red Cross. Other authors are also very critical of the blood group diet. In their opinion, it could not be shown, for example, that there is a connection between the blood group and the tolerability and health-promoting properties of certain foods.

If you want to lose weight healthily and permanently and without  the yo-yo effect  , then a varied diet with lots of  fruit  and  vegetables  and an appropriate exercise program is certainly the best way to achieve your dream figure. In all likelihood, the blood group does not play a role.

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