Why Am I This Type?

February 4, 2011 at 12:36 pm

By Billie Rubin, Hemoglobin’s Catabolic Cousin, reporting from the labs of Stanford Blood Center

This is one of several questions that we’re often asked by community members. Our ABO (blood type) identity, whether we’re O, A, B, or AB, is inherited from our parents. The ABO genes we inherit produce the antigens (chemical structures like proteins, carbohydrates or glycolipids) that are attached to the surface of red cells. Other things in nature also have these A & B antigens (bacteria and pollen, for example).

After birth, when our bodies are exposed to a foreign antigen (one you did not inherit), our immune system makes antibodies against it. If you are type A, then B is foreign to you and you make anti-B. If you are type O, then both A & B are foreign to you and you make anti-A and anti-B. These antibodies float around in the plasma portion of the blood. Both the ABO antigens on the red blood cells and the anti-A and/or anti-B in your plasma, determine your ABO Identity. Being Rh + or – is inherited separately from our ABO genes and it’s a little different. Read more about that here.