What are blood types?

Your blood type (or blood group) is determined by the chemical structures on the outside of your red blood cells. These chemical structures are called antigens.

Your blood type is decided by the genes you inherit from your parents.

What are the different blood types?

Your blood group depends on your ABO group, and your Rhesus group.

ABO blood group

There are 4 different blood types — A, B, AB and O. These names indicate whether your red blood cells carry the:

• A antigen — Type A
• B antigen — Type B
• A and B antigens — Type AB
• neither antigen — Type O

Blood types in Australia

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

The table below lists each of the blood types, including:

• how common they are across the Australian population
• what blood types they are compatible with

Blood type	How many Australians have it	Compatible blood types
O+	38%	O-, O+
O-	7%	O-
A+	32%	A+, A-, O+, O-
A-	6%	A-, O-
B+	12%	B+, B-, O+, O-
B-	2%	B-, O-
AB+	4%	AB+, AB-, A+, A-, B+, B-, O+, O-
AB-	1%	AB-, A-, B-, O-

O- blood can be safely given to anyone, regardless of their blood type.

Rhesus group

The Rhesus group or Rh group contains around 50 different antigens that can be found on the surface of your red blood cells.

The most important antigen is RhD.

Each of the 4 blood groups can be classified as either:

• Rhesus-positive — you have the RhD antigen
• Rhesus-negative — you don't have the RhD antigen

More than 4 out of 5 Australians are Rhesus positive.

Why should I know my blood type?

Knowing your blood type means that you can:

• have a safe pregnancy
• help others when there are blood shortages

Blood type and blood transfusions

If you need a blood transfusion, you will have your blood tested for blood group and antibodies to make sure the donor blood you receive is compatible with your blood.

Blood from a different blood type has different antigens on the blood cells. This means that when your immune system recognises the donor blood cells, it could attack them.

If you need a blood transfusion, in an emergency and there is no time to match your blood type, you will be given O- blood. This is because O- blood has no antigens, and can be safely given to anyone.

Receiving the wrong blood type in a transfusion can be life threatening and you would need treatment quickly. However, it is extremely rare for this to happen.

Blood type and pregnancy

It is also possible for a pregnant person and their baby to have incompatible blood types. If you have a different blood type to your baby, you may need treatment while pregnant.

You may have a Rhesus negative blood type while your unborn baby has a Rhesus positive blood type. This can lead to Rhesus factor disease.

Rhesus factor disease is when your immune cells attack your baby's rhesus positive cells. This can lead to severe anaemia or death.

It can be prevented by treating you with anti-D immunoglobin. This neutralises your baby's rhesus positive blood cells in your blood stream before your immune system produces antibodies.

Donating blood

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:

• injuries
• severe burns
• blood diseases

Donating blood'can save someone else's life. It can also be turned into different medical treatments, depending on which blood type you have.

Resources and support

Visit the Australian Red Cross Lifeblood website or call 13 14 95 to:

• learn more about blood groups
• find out if you're eligible for blood donation

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with 24 hours a day, 7 days a week.