There are four primary blood types: A, B, AB, and O.
Your blood type is inherited from the genes passed down by your parents.
Each blood type can either be RhD positive or RhD negative, giving a total of eight possible blood types.
Antibodies and Antigens
Blood is made up of red blood cells, white blood cells, and platelets, all suspended in plasma.
Your blood type is determined by the specific antibodies and antigens it contains.
- Antibodies are proteins in plasma that play a role in the immune system. They detect foreign invaders, such as bacteria or viruses, and signal the body to destroy them.
- Antigens are protein molecules found on the surface of red blood cells.
The ABO Blood System
The four main blood groups are classified according to the ABO system:
- Group A: Has A antigens on red blood cells and anti-B antibodies in plasma.
- Group B: Has B antigens on red blood cells and anti-A antibodies in plasma.
- Group O: Lacks A and B antigens on red blood cells but has both anti-A and anti-B antibodies in plasma.
- Group AB: Has both A and B antigens on red blood cells and no antibodies in plasma.
Group O is the most common blood type, with approximately 48% of the UK population having this blood type.
Receiving the wrong ABO type can be harmful. For example, if someone with type B blood receives type A blood, their anti-A antibodies will attack the A cells, which can cause serious complications.
This is why type A blood should not be given to someone with type B blood, and vice versa.
Group O red blood cells can be given to any group because they don’t have A or B antigens.
The Rh System
In addition to the ABO system, red blood cells may also carry a protein known as the RhD antigen.
If you have this antigen, your blood type is RhD positive; if not, it’s RhD negative.
This adds another layer, resulting in eight possible blood types:
- A RhD positive (A+)
- A RhD negative (A-)
- B RhD positive (B+)
- B RhD negative (B-)
- O RhD positive (O+)
- O RhD negative (O-)
- AB RhD positive (AB+)
- AB RhD negative (AB-)
O RhD negative blood is commonly used in emergencies because it lacks A, B, and RhD antigens, making it safe for most recipients, regardless of blood type.
Blood Group Testing
To determine your blood type, a blood sample is mixed with different antibody solutions.
If your red blood cells clump when mixed with a specific antibody, you have the corresponding antigen.
For example, if your blood reacts to anti-B antibodies, your blood type is B, because you have B antigens.
If your blood doesn’t react to either anti-A or anti-B antibodies, your blood type is O. Additional tests are conducted to confirm the exact blood type.
Before a blood transfusion, your blood is tested against the donor’s blood to ensure compatibility with their ABO and RhD type.
If no reaction occurs, the transfusion can proceed with the matching blood.