What blood type is considered the universal donor?

What blood type is considered the universal donor? O negative is the standard universal donor type for red blood cells.

O-negative red cells lack A and B antigens and also lack the Rh D antigen. Because a recipient’s immune system is less likely to attack those cells based on the major ABO and Rh systems, hospitals may use them when there is no time to determine a patient’s blood type, such as during severe bleeding.

The term “universal donor” has limits. It mainly refers to red-cell transfusions and assumes that clinically important antibodies from other blood-group systems are absent. Blood banks still prefer fully matched and cross-matched blood whenever possible, because O-negative supplies are limited.

A frequent confusion concerns plasma. The compatibility pattern reverses for plasma: AB plasma is often called universal donor plasma because it lacks anti-A and anti-B antibodies. AB positive is instead known as the universal recipient type for red blood cells. O-positive blood can help many patients, but it cannot safely serve every Rh-negative recipient.