I also considered this. The patient had two type and screens prior to the transfusion that both resulted as A pos and negative antibody screen. The post transfusion type and screen resulted as anti-A (4+), anti-B (neg), anti-D (4+), A1 (neg), B (3+), and a positive antibody screen. If an anti-A1 were present, wouldn't there be an ABO discrepancy?