What are blood types? Our blood group describes important characteristics of our red blood cells and determines whether our blood matches that of other people – which is especially vital information for donating blood and blood transfusions.
Our blood has very special characteristics, which we inherit from our parents and which are associated specifically with our blood group. Knowing our blood group is especially important when it comes to blood transfusions. If, for example, in the case of illness or injury, you receive someone’s blood that does not match your own, this can lead to dangerous blood clots.
Interestingly, our blood group is also becoming increasingly important in medical research because experts are studying connections between individual blood groups and certain diseases, such as type 2 diabetes. There also seems to be a link between severe COVID-19 infections and blood groups.
Which characteristics are assigned to which blood group types and what is the most common blood type? Who can donate blood to whom? What blood type am I? We answer these frequently asked questions in this article to provide you with more insights on a topic that is gaining ground when it comes to medical research. You can also find out more about how blood groups are associated with the severity of COVID-19 infections: Do certain blood groups protect against severe COVID-19 infections? Read on to find out!
What Are Blood Types?
On the basis of individual characteristics on the surface of red blood cells, our blood can be divided into different blood group types. The two most important systems are the AB0 system and the Rhesus system.
Did you know that the Austrian doctor Karl Landsteiner found out that different peoples’ blood often – but not always – clumps together, and that he developed the blood groups A, B, AB, and 0 from this? For his contribution to medicine, he received the Nobel Prize for Medicine in 1930. In 1940 he established the Rhesus factor as another important blood characteristic. World Blood Donor Day is held annually on his birthday on June 14.
What Is Meant by the ABO Blood Group System?
All red blood cells (erythrocytes) are surrounded by a sheath. On this sheath are various proteins that give the sheath a specific structure. It is because of these proteins, the antigens A and B, that we can distinguish the red blood cells of one person from those of another.
In the AB0 blood group system, blood is divided into the four blood group types A, B, AB, and 0, according to the antigens on the red blood cells:
- Blood group A has antigen A on the red blood cells
- Blood group B has antigen B on the red blood cells
- Blood group 0 has no antigens on the red blood cells
- Blood group AB has both antigens A and B on the red blood cells
At the same time, all people have special proteins in their blood plasma that can recognize the blood of a foreign blood group. These are called blood group antibodies. The blood group antibodies are Y-shaped and can combine with antigens of a foreign blood group and then clump together.
A person with blood group A has antibodies against blood group B. When blood is donated, these two types of blood would therefore clump together.
- Blood group B has antibodies against blood group A
- Blood group AB has no antibodies
- Blood group 0 has both antibodies A and B
A and B
A and B
Blood plasma, which is transparent and slightly yellowish, is liquid and consists of 91 percent water. The rest of our blood plasma is made up of nutrients, hormones, minerals, and more than 120 different proteins, which, as antibodies, are responsible for blood clotting and protecting us against infections. Our blood gets its red color from the red blood cells (erythrocytes), which are one of the solid components in our blood. They transport oxygen and carbon dioxide through our body.
How Does the Rhesus System Work?
In addition to the AB0 blood group system, there are others, including the Rhesus system. When talking about the Rhesus system, it is important to note the Rhesus factor D. This is a protein substance that can also be found on the surface of the red blood cells. Most people have this Rhesus factor (also called antigen D), meaning they are Rhesus-positive (Rh+). Some people lack it and are therefore deemed Rhesus-negative (Rh-). In the United States, this applies to about 15 percent of the population.
In practice, doctors mark the Rh-positive blood group with “+” and the Rh-negative blood group with “–.” For example, the designation “blood group 0+” means that it is “blood group 0, rhesus factor positive.”
The Rhesus factor also indicates whether the blood of two people is compatible when mixed – such as the blood of a mother and child during pregnancy or during birth. If they have different Rhesus factors, this can lead to problems.
If a Rhesus-negative woman is expecting a Rhesus-positive child, the mother’s blood can form antibodies against the child’s Rhesus factor and impair its healthy development. In Rhesus-negative pregnant women, a blood test is therefore routinely carried out to determine the baby’s Rhesus factor. If the baby is Rh-positive, the mother is injected with an anti-D prophylaxis. This prevents the mother from forming antibodies against the baby’s blood.
Blood Group Types: What Is the Most Common Blood Type?
If you combine the AB0 system and the Rhesus system, there are a total of eight different blood group combinations – namely, 0–, 0+, A–, A+, B–, B+, AB–, and AB+, some of which are more common in certain parts of the world than in others.
In central Europe, blood groups A and 0 are the most common, while blood groups B and AB are less common. Most people have Rhesus-positive blood. In the United States, 0+ is the most common blood type, with roughly one in three people having this blood type. The rarest blood type nationwide is AB– – only just over one percent of people have this blood type in the United States.
Why Are Some Blood Groups More Common?
Experts suspect that our blood groups have existed for several million years. For example, a team of researchers has found that 40 different primate species (including apes, great apes, and prosimians in addition to humans) have blood groups within the AB0 system. This indicates that the blood groups formed even before apes and humans evolved apart.
Researchers suspect that these different blood groups developed because they brought evolutionary advantages against certain diseases.
How Does Blood Group 0 Protect against Malaria?
Experts have identified an example of an evolutionary advantage when it comes to malaria and blood group 0. In Africa, for example, the infectious disease is very widespread, and there are also a particularly large number of people with blood group 0. Various studies have found that people with blood group 0 are less severely affected by malaria when they contract it.
Experts assume that the reason for this is the role of the blood group antigens. The blood group antigens on the red blood cells often serve as an entry point to the body for bacteria, viruses, and parasites (such as the Plasmodium pathogen in malaria). Since blood group 0 has no such blood group antigens, the malaria pathogen probably has worse chances of survival than in other people.
Malaria has had a major impact on human development because it mainly affects children. According to the World Health Organization (WHO), more than 400,000 people died from malaria in 2019 – 67 percent of whom were children under the age of five. Only the children who survive this disease can later produce children of their own. Since children with blood group 0 are more likely to survive the disease, they are by extension more likely to pass on their genetic characteristics (such as their blood group) to their children. This explains the high proportion of people with blood group 0 in areas affected by malaria today.
Does Blood Type Affect the Risk of Severe Illness from COVID-19?
COVID-19 and its effect on our bodies is currently being intensively researched. In particular, the question of why the virus triggers severe and life-threatening disease in some people, while others experience few or even no symptoms, is driving various scientific research projects at the moment.
In this context, blood group types have also been an important focal point: A Chinese research team found that many people with severe COVID-19 have blood group A, while blood group 0 seems to offer a level of protection against the virus.
The reason for this connection seems to lie in our genes: A recent study suggests that characteristics that determine our immune defense are inherited together with our blood group. The research team examined the genetic material of seriously ill patients and compared it with the DNA of healthy people. They found two short gene segments, whose variants increase the risk of severe COVID-19 infections. One of the gene segments is located exactly in the area of our DNA that determines a person’s blood group.
This study therefore explains why our blood group could influence the severity of a COVID-19 infection. The exact reasons behind this still need to be researched further.
One hypothesis deals with COVID-19 and blood clotting – COVID-19 increases blood clotting – which can potentially lead to pulmonary embolisms or strokes. People with blood group 0 are less likely to experience blood clotting than people with other blood group types – this could be one reason why a COVID-19 infection is less severe among these people.[14, 15]
What Blood Type Am I?
Do you not know your blood group? You can find out your blood group accurately with a blood test at your doctor’s practice or with a quick test from the drugstore.
To carry out ABO typing, a blood sample is needed. To find out your blood group, your red blood cells are mixed with different antibody solutions – namely, with antibodies against type A and B blood. After this, lab experts check your sample and observe whether blood cells stick together. If they do stick together, it means that your blood has reacted with one of the antibody solutions.
Following on from this, the liquid part of your blood sample without cells (known as the serum) is mixed with blood that is known to be type A and type B. People with type A blood have anti-B antibodies. People with type B blood have anti-A antibodies. Both types of antibodies are found in type O blood.
Rh typing is similar to ABO typing – apart from the fact that the tests carried out on your blood sample will determine whether you have the Rh factor on the surface of your red blood cells. If you do, this means that you are Rh-positive.
There are also various situations in which you can find out your blood group.
When Can I Find Out My Blood Group Type?
Your blood group is often determined in the following situations:
- Pregnancy screening
- Blood donation
- Blood transfusion (before an operation or in the case of severe anemia)
- Organ transplants
Where Is My Blood Group Noted?
If your blood group has ever been determined, it is noted in your:
- Maternity passport
- Blood donor card
Blood Group Types: Who Can Donate Blood?
When talking about donating blood, you might often hear the terms “universal donor” and “universal recipient.” These are the most important facts you should know about these terms:
- People with blood type 0 are universal donors. This mean they can donate blood to the other three blood groups, but they can only receive blood from an 0-type donor themselves.
- People with blood type AB are considered universal recipients. They can receive blood from all other blood types, but can only donate blood within their own blood type.
You should note that people with Rhesus-negative blood can also only receive blood with Rhesus factor negative (Rh–). People with a Rhesus-positive blood group, on the other hand, can receive Rh– and Rh+ blood.
What Are Blood Types – at a Glance
What Are Blood Types?
Our blood group is determined based on individual characteristics on the surface our red blood cells. Based on these characteristics, our blood can be divided into different blood group types. The two most important systems are the AB0 system and the Rhesus system.
Which Blood Groups Are There?
If you combine the AB0 system and the Rhesus system, you get eight different blood groups – namely, 0–, 0+, A–, A+, B–, B+, AB–, and AB+. The most common blood type in the United States is 0+.
Your blood group tells you whose blood your blood is compatible with.
What Blood Type Am I?
You can find out your blood group through a blood test at your family doctor’s or with a quick test from the drugstore.
There are also various situations in which you could find out your blood group. These include prenatal care, blood donation, preparing your emergency ID card, blood transfusion, or an organ transplant.
You can find your blood group in your maternity passport, blood donor card, or emergency ID card.
Who Can Donate Blood to Whom?
People with blood group 0 are universal donors, while people with blood group AB are universal recipients.
People with a Rhesus-negative blood group can also only receive blood with Rhesus factor negative (Rh–). People with a Rhesus-positive blood group, on the other hand, can receive Rh– and Rh+ blood.
Does Blood Type Affect the Risk of Severe Illness from COVID-19?
Experts have observed a link between different blood groups and the severity of a COVID-19 infection. Studies suggest that people with blood group A have more severe infections than others, whereas blood group 0 seems to have a level of protection against the virus.
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