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Blood group compatibility: Do you know your blood group type?

Emeh Joy

Do you know your blood can save lives? However, while everyone's blood is typically composed of the same basic parts, there are a variety of blood types.

You need to know your blood group type so that you can determine the group you can donate blood to or the group that can donate to you.

Because an individual's blood type depends on the genes inherited from parents, this causes a variation in blood composition between individuals.

Blood types are differentiated by differences in structure and antigen present on the surface of the red blood cells.

What are blood types and what makes a blood type?

There are eight different types of blood group, and an individual's blood type would depend on the genes inherited from parents.

The human body contains about 4 to 6 litres of blood with the blood composed of different cells floating within a fluid which is called "plasma".

The main components of blood are:

  • Red blood cells which are the carriers of oxygen
  • White blood cells which play the key role in the body's immune system
  • Blood platelets which aid in blood clot
  • Blood plasma, which is the yellowish fluid that contains proteins and salts.

Red blood cell compatibility table

What differentiates blood and groups them into types is the unique combination of protein molecules called antigens and antibodies.

What are antigens and antibodies?

Antibodies are proteins found in the blood plasma, which the immune system (white blood cells) produces to fight against a foreign agent.

They are part of your body's natural defence. Once your body notices an invasion by a foreign agent such as germs, it mobilises the antibodies to fight against the foreign agent.

Antigens, on the other hand, are molecules found on the surface of red blood cells and can be either proteins or sugars. Among the functions of antigens in the blood are:

  • To maintain the structure of red blood cells
  • To transport other molecules in and out of the cells
  • To detect unwanted to abnormal cells that can cause sickness

Generally, scientists classify blood types using two types of antigens:

Both antigens and antibodies play an important role in the immune system's defence mechanism.

The different blood group types and blood donor compatibility

There are eight different blood types:

  • A+: A positive is one of the most common blood types, and someone bearing this blood type can give out blood to people who are A positive (A+) or AB positive (AB+).
  • A-: A negative is a rare blood type. However, people with this blood type can give out blood to people with A or AB blood type (both negative and positive).
  • B+: B positive is a bit common but not as much as A positive. Individuals with this blood type can donate blood only to people who are B positive (B+) or AB positive (AB+).
  • B-: People with B negative blood type can donate blood to people with B+, B-, AB+ and AB- blood types.
  • AB+: People with AB positive blood type are known as universal recipients because they can receive from any blood plasma type. But, they can only donate to AB+ blood group.
  • AB-: AB negative is the least common blood type. People who have this blood type can give out blood to people with blood groups AB+ and AB- and can receive from all negative blood groups.
  • O+: Just like A positive, O positive is quite common too. Someone with this blood type can give out blood to any positive blood group. They can only receive blood from O- and O+.
  • O-: Someone with O negative blood type can give blood to anyone. However, they can only receive from someone with O negative.

Understanding the ABO Blood Group System

Scientists use two types of antigens to classify blood types, and one of these is the ABO antigens.

The ABO blood group is a system that classifies blood types according to the different types of antigens which are present on the surface of the red blood cells and also the antibodies in the blood plasma.

Understanding the presence of antigens in the red blood cells and antibodies in the blood plasma

With this, the ABO group is classified into four:

Group A: With this blood group, A antigen is present on the surface of the red blood cells while the blood plasma contains anti-B antibody. What this means is that the anti-B antibody in the plasma will attack any blood cell that contains B antigen.

Group B: B antigen is present on the surface of red blood cells for this blood group. Also, the plasma has anti-A antibody, which means it would launch an attack on any blood cells that contain A antigen.

Group AB: AB group has red blood cells that have both A and B antigens. However, the blood plasma has neither anti-A nor Anti-B antibodies. Hence, individuals with this blood type can receive blood from any ABO blood type.

Group O: Group O blood plasma contains both anti-A antibodies and anti-B antibodies (opposite of Group AB). However, the surface of the red blood cells doesn't contain A antigen or B antigen.

What this means is that since it has both anti-A and anti-B antibodies, it can't receive blood from any group that has Antigen or B antigen. However, since its blood cells do not contain A antigen or B antigen, it can give out blood to any ABO blood type.

The second classification and third type of antigen, which scientists use to classify blood types is the Rh antigen. It is either you have the Rh antigen (meaning your blood type is positive "Rh+"), or you don't (which means your blood type is negative, "Rh-").

Why is blood type important?

An Austrian scientist by the name, Karl Landsteiner discovered blood groups in 1901. Before then, doctors had no idea that people have different blood types. This ignorance led to many deaths via transfusion.

Grouping blood into types saves lives as it makes for safety after blood transfusion. Mix up of incompatible blood types can be fatal

But now, health professionals know that when blood from two different or incompatibility blood groups mix, the blood can clump. The result can be fatal as the recipient's antibodies launch an attack on the donor's blood cells (with opposing antigen).

Thus, for a blood transfusion to be effective and safe, it is essential that the donor's blood and that of the recipient match.

While it is best that a donor and recipients blood match exactly and belong to the same blood group, it is not a must. The donor doesn't always need to have the exact same blood type as the recipient. Their blood types only have to be compatible.

For instance, in the absence of an A positive donor, an O positive or O negative donor can still donate to an A positive recipient.

How to know your blood type: Blood group test

You might be wondering how you can tell your blood group type. The answer is simple; you have to run a blood test to determine your blood type.

Your red blood cells will be mixed with different antibody solutions. The reaction of this mixture will tell your blood type.

If for instance, the solution carries anti-A antibodies and you have A antigens in your blood, the mixture will clump together showing that your blood group is A.

Suppose your blood doesn't react to any of the anti-A or anti-B antibodies. In that case, yours should be blood group O. Series of tests will be carried on your blood sample using different types of antibody to identify your blood group.

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