A crossmatch also has limitations:
-Will not detect errors in patient identification (unless a previous record exists)
-Will not detect ABO mix-ups if blood types are compatible (can crossmatch group A donor blood for an AB recipient)
-Will not detect Rh errors (can crossmatch Rh+ donor blood with Rh negative recipient with no reaction if the patient has no anti-D)
-Will not detect all recipient antibodies to donor antigens (antibody may be too weak to detect, but still cause transfusion reaction such as the Kidd antibodies)
-Will not prevent alloimmunization of recipient (only ABO and Rh antigens matched - patient can potentially make antibody to all the other antigens) This is why many of the discovered antibodies are found in multi-transfused patients.