If you’ve ever needed a blood transfusion, or donated blood, you probably would have been asked your blood type. While it was once thought all blood was the same, we now know there are different types of blood, called blood groups. Transfusions between blood groups can be catastrophic, even deadly, so knowing the blood type of donors and recipients is of the utmost importance.
Our bodies contain trillions of red blood cells. Each is covered in an array of proteins and sugars, inherited from our parents, which determine our blood group. We can all be classified into group A, B, AB or O, based on which sugars coat our red blood cells.
We’re also classified as positive or negative, based on whether our blood cells carry a protein called the Rhesus D (RhD) antigen. These two blood group systems (ABO and Rh) give us the eight main blood types: O-, O+, B-, B+, A-, A+, AB-, AB+.
But there are also more than 300 different antigens – proteins and sugars that activate the immune system – expressed on red cells and 36 recognised blood group systems. And they’re just the ones we know about.
While most people know they are, for example, A+ or O-, few people will know (and never need to know) what their expression of other red cell antigens are.