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Human blood belongs to one of four main blood groups: A, AB, B, and O. Each of these groups can also be positive or negative for the Rhesus factor, which means you can have an A positive or an A negative blood, just as you can have for AB, B, and O blood groups. But what does this grouping mean to you, and why should you care?
Blood antigens and antibodies
Blood grouping is based on the presence or absence of antigens and antibodies in your blood. Antigens are proteins found on the red cell surface, while antibodies are natural proteins in plasma.
An antigen triggers your immune system to generate antibodies. The antibodies alert your body to destroy the antigens they recognise as foreign.
Red blood cells have different types of antigens used to group them. The most commonly recognised blood groups are:
- The ABO blood grouping system
- The Rhesus (Rh) blood grouping system
ABO system
In the ABO system, the blood group is based on the presence or absence of the A and B antigens. There are four blood groups in this grouping system.
- Group A - has A antigen and anti-B antibody
- Group B - has B antigen and anti-A antibody
- Group AB - has both A and B antigens but no antibodies
- Group O - has no antigens but has both anti-A and anti-B antibodies
Group O blood is the most common blood group in Nigeria. More than half of Nigerians (53%) have group O blood. Very few (less than 4%) have group AB blood.
According to the ABO grouping system, your body tolerates the antigens in your blood and produces antibodies against the antigens you do not have.
ABO blood compatibility
The ABO blood grouping determines who you can donate blood to or receive blood from. This is known as blood compatibility or the capacity of blood from two individuals to combine without destroying each other.
Blood transfusion can safely be done only between two compatible blood groups. This means you must only receive blood your body will not react to.
For example, if you have blood group A, your safest option is to receive blood group A. If you receive blood from an incompatible blood group, say group B, your anti-B antibodies will attack the B antigens on the donor red cells, which could be life-threatening.
A safer option will be to receive group O blood. Because the group O blood has no antigen, it can safely be given to people with any other blood group.
The ABO blood grouping compatibility is summarised as follows:
- Group A: individuals with this blood group can donate to individuals with group A or AB blood but can receive blood only from individuals with group A or O blood.
- Group B: individuals with this blood group can donate to individuals with group B or AB blood but can receive blood only from individuals with group B or group O blood.
- Group AB: individuals with this blood group can donate only to individuals with group AB blood but can receive blood from any other blood group.
- Group O: individuals with this blood group can donate to individuals with any blood group but can receive blood only from individuals with group O blood..
Rh system
In the Rh blood grouping system, the blood group is classified depending on the presence of the Rhesus (Rh) factor. The Rh factor is coded for by the D antigen. So if your blood has the Rhesus factor, you are Rhesus-D positive (RhD-positive). If it does not, you are Rhesus-D negative (RhD-negative).
The ABO and Rhesus grouping systems are often taken together to give your blood type. That means your blood group can be one of the following:
- O-negative (O-)
- O-positive (O+)
- A-negative (A-)
- A-positive (A+)
- B-negative (B-)
- B-positive (B+)
- AB-positive (AB+)
- AB-negative (AB-)
Individuals with AB-positive blood are considered universal recipients because they can receive blood from any other blood group, while a person with type O-negative blood is considered a universal donor because their blood can be safely given to anyone.
Rhesus compatibility
Rhesus compatibility is not often considered in blood group grouping and crossmatching for blood transfusion, but the compatibility between a pregnant woman and the foetus is is very important.
A child can inherit the Rhesus-D antigen from either the mother or father. If the mother is RhD-negative but the child is RhD-positive due to inheritance of Rhesus-D antigen from the father, there will be Rhesus incompatibility between the mother and child.
The mother may produce anti-D antibodies that react with the child’s RhD antigens, causing severe complications for the child. This is preventable. Speak with your obstetrician or gynaecologist to discuss the preventions if you are a RhD-negative mother.
How to check your blood group
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You can check your blood group by visiting a registered laboratory. A laboratory scientist will collect your blood and test it for the blood group antigens that we've outlined.
The scientist will tie a tourniquet around your wrist or arm and insert a syringe into a vein to collect your blood into a sample bottle or syringe.
Your red blood cells will then be mixed with reagents containing antibodies against the common red cell antigens. That is, anti-A and anti-B antibodies—a third reagent containing anti-D antibody test0s for Rhesus-D (RhD) antigen.
The nature of the reaction between your red blood cells and the reagents determines your blood group. Remember, blood group antigens will react with their corresponding antibodies.
Therefore, if you have A antigens on your red blood cells, they will react with anti-A antibody reagents and clump together. The reaction will appear like pellets. If the antigens on your red blood cell are different from the antibodies in the reagent, they will not react; your blood will remain fluid.
If your blood reacts to anti-A and anti-B antibody reagents, it means you have blood group AB. Individuals with blood group O do not have antigens on their red blood cells, so their blood does not react with anti-A and anti-B antibodies.
Conclusion
Knowing your blood group is important for safe blood transfusion and pregnancy. It helps you to avoid or prevent severe complications that may affect individuals receiving blood transfusion or newborns. It is also important during emergencies as it will ensure timely treatment. Your knowledge could help you determine your susceptibility to certain diseases and your ancestry. Check your blood group today.
