How Blood Type Is Determined And Why You Need To Know

Blood types are determined by the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body.  Since some antigens can trigger a patient’s immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching. Do you know what blood type is safe for you if you need a transfusion?


There are four major blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells. In addition to the A and B antigens, there is a protein called the Rh factor, which can be either present (+) or absent (–), creating the 8 most common blood types (A+, A-, B+, B-, O+, O-, AB+, AB-).

The importance of knowing your blood type is to prevent the risk of receiving an incompatible blood type if a transfusion is needed. If the wrong blood types are mixed, it can lead to a clumping of blood cells that can be potentially fatal.

Type A Negative

Only 1 in 16 people have A negative blood.

If you have A negative blood you can donate to anyone with a blood type of A or AB regardless of the positive or negative, however if you have A negative blood you can only receive A- or O- blood.