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Blood types

6-minute read

What are blood types?

A person’s blood type, also known as their blood group, is the chemical structure on the outside of their red blood cells. The chemicals on the outside of the blood cells are called antigens.

Someone’s blood type is decided by the genes they inherit from their parents. Different blood types do not mix.

A blood test is done to find out the blood type before a blood transfusion, major surgery or having a baby. This is because it is very dangerous if you are given the wrong blood type. If someone receives blood with the wrong sort of chemicals, the body’s immune system could attack it. It is also possible for a mother and her baby to have incompatible blood types, and this will need treatment while the mother is pregnant.

If you need a blood transfusion and you do not know your blood type, or your blood type is not available, then there are other blood types that can be safely given to anyone.

The different blood types

There are 4 different blood types – A, B, AB and O. These names indicate whether the blood’s red cells carry the A antigen, the B antigen, both A and B antigens, or neither antigen.

Each of the 4 blood groups can be classified as either Rhesus positive or Rhesus negative. The Rhesus system looks at different antigens on the surface of the red blood cells. If there is an antigen called the RhD antigen, the blood is Rhesus positive. If there is no RhD antigen, the blood is Rhesus negative. More than 4 out of 5 Australians are Rh positive.

The most common blood type in Australia is O positive and the least common is AB negative.

The table below lists each of the blood types, including how common they are across the Australian population.

Blood type How many Australians have it About this blood type
O+ 40% This is the most common blood type.
O- 9% O- can be safely given to any patient, regardless of their blood type.
A+ 31% Type A platelets (a component of blood that is important for clotting) can be safely given to any patient.
A- 7%
B+ 8% Type B is more common in South Asian and black communities.
B- 2%
AB+ 2%
AB- 1% This is the rarest blood type.


What if I need a blood transfusion?

People may need a blood transfusion if they lose a lot of blood; their blood is low in certain components such as red cells, platelets or plasma; because they have a medical condition such as cancer, anaemia or a bleeding disorder; or because they are having surgery.

If you need a transfusion, you will receive blood that has been collected by Australian Red Cross Lifeblood from voluntary donors. All blood is rigorously checked for infections such as HIV and hepatitis. You will also have careful identification checks before the transfusion to make sure you receive the right blood type.

Receiving the wrong blood type in a transfusion is extremely rare. If you did get the wrong blood type, you could have a serious reaction. This could be life threatening so you would need treatment quickly.

Donated blood can be turned into different medical treatments, depending on which blood type you have. For example, whole blood from type A, type O positive and type O negative is always needed. People with type AB or type B can donate plasma, which is vital for patients with injury, severe burns or blood diseases.

Donating blood can save someone else’s life. To find out if you’re eligible, and to learn more, visit the Australian Red Cross Lifeblood website or call 13 14 95.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: June 2021

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