A hemolytic reaction can occur between type O and type A blood. Because the mechanism of hemolytic reaction is antigen-antibody reaction, when antigen and antibody combine, it will lead to red blood cell lysis and destruction and hemolysis will occur. type O blood has no A antigen and no B antigen on the red blood cell membrane, however, there are anti-A antibody and anti-B antibody in the serum, and type A blood has A antigen on the red blood cell membrane and anti-B antibody in the serum, when type O blood and type A blood are mixed, the anti-A antibody in type O blood will combine with the A antigen in type A blood, leading to red blood cell lysis and destruction. Hemolysis between type O blood and type A blood is very common in neonatal hemolysis, especially in mothers with type O blood, and if the fetus has type A or type B blood, the fetus is prone to hemolytic reactions at birth due to maternal-infant blood group incompatibility.