O blood type must be transfused when transfusing blood type O. Human blood types can be roughly divided into O, A, B and AB. O blood type refers to the surface of red blood cells that contain neither A antigens nor B antigens, which is commonly known as the universal blood donor, but because it contains anti-A antibodies and anti-B antibodies in the plasma, it may lead to hemolysis of red blood cells in the recipient to varying degrees, so O blood type transfusion RH positive O type can not be transfused to RH negative O blood, RH negative O type can be transfused in small amounts to RH positive O blood, including RH positive A, B and AB, China’s RH system is positive, the total number of RH system negative on average will not exceed 3 per 1,000.