The universal donor blood type is **Type O negative** (O-). Individuals with this blood type are considered universal donors because their blood lacks both A and B antigens on the surface of red blood cells, and they do not have the Rh factor (the positive or negative sign). As a result, their blood is less likely to cause an immune reaction when transfused into recipients of different blood types.
Because Type O negative blood lacks A, B, and Rh antigens, it can be safely transfused to individuals with any ABO and RhD blood type, including Type A, Type B, Type AB, and Type O recipients. This makes Type O negative blood in high demand for emergency situations when the recipient's blood type may not be immediately known.
It's important to note that while Type O negative blood is considered the universal donor for red blood cell transfusions, there is no universal plasma donor because plasma contains antibodies against the ABO blood group antigens, making compatibility crucial for plasma transfusions.