To find out your blood group, a sample of your blood has to be taken and tested. However, GPs do not routinely check people's blood groups.
You can also find out your blood group by giving blood.
Healthcare professionals sometimes need to know a person's blood group for medical reasons.
If you need a blood transfusion, the blood group you receive must be compatible with your own blood group.
Your blood will therefore be tested before you receive a blood transfusion to make sure you're given a matching blood group.
Giving someone blood from the wrong group can potentially be life threatening.
If you're pregnant it's important to know if you're rhesus negative or positive. Find out more about rhesus disease.
Healthcare professionals will also check a person's blood group before they:
- give blood
- have an operation
- donate an organ for transplant
Your blood group will be checked if you give blood through NHS Blood and Transplant, and it will be recorded on your official donor card.
This is so your blood can be matched to someone with the same blood group or a group that's compatible.