What Are Blood Groups and Why Do They Matter?

Donor blood must be compatible with the patient’s blood to minimise the chance of a transfusion reaction. Toby Melville/Reuters

Danielle Andrew 07 Mar 2017, 18:01

How were blood groups discovered?

Transfusion has been practised intermittently since the 1660s. But blood groups weren’t discovered until 1900, before which it was assumed that all blood was of the same type.

This led to some catastrophic transfusions of animal blood into humans in attempts to transfer certain qualities (for example, so the recipient would become meek like a lamb). There were also some fatal transfusions between humans.

For this reason, the practice was banned in the UK and France for more than 100 years.

In 1900, physician Karl Landsteiner’s experiments showed that some people’s red cells “reacted” with plasma samples from other people, while others did not. This led to him describing the ABO system, the most important blood group system and the basis of safe modern transfusion.

After receiving the 1930 Nobel Prize for Medicine for this work, Landsteiner was experimenting with the blood of Rhesus monkeys when he discovered what is now known as the RhD antigen.


If we need to transfuse blood from one person to another, we want to give donor blood that is compatible with the recipient’s blood to minimise the chance of a transfusion reaction.

So if a person is group A, this means she can receive a red cell transfusion from either a group A or a group O donor. She should not receive group B or AB red cells, as she has naturally occurring antibodies (proteins formed as part of the immune response) that will likely cause a transfusion reaction, which may be serious – even fatal.

Around 31% of Australians are A+. It’s the second most common blood group after O+, which make up 40% of the Australian population.

O negative people are universal donors. www.shutterstock.com

Group O negative people are called “universal donors”. Their red cells express neither group A nor B sugars, nor the RhD antigen, and so are unlikely to cause a reaction in recipients.

Emergency departments and some ambulances carry a stock of O negative blood, because in an emergency this is the safest blood to give a critically ill, bleeding patient of unknown blood type. Only 9% of the Australian population are O negative.

The Australian Red Cross Blood Service needs a diverse group of blood donors to meet the needs of our increasingly diverse patient population.

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