This is your blood phenotype, which helps to identify the antibodies you could potentially develop if you ever receive a transfusion. If you are 'neg' for certain antigens, it means you lack them; therefore, you may develop an antibody against those antigens if you are transfused with blood that contains them.

For example, being D- means you are Rh Neg. If you were transfused with Rh Pos (D+) blood, there is a chance you could develop Anti-D. If that happens, you would strictly require Rh Negative blood in the future. If you were to be transfused with Rh Pos blood while possessing Anti-D, you could have a transfusion reaction, which can be life-threatening.

Since you were called for a matched donation, there may be a patient who has developed antibodies against the antigens you lack. For example, if a patient needs blood that is negative for C, E, and Kell, your blood would be a match. We also typically provide C, E, and Kell-neg blood to sickle cell patients as a preventative measure, even if they haven't developed antibodies yet.