A man whose blood group is not known meets with a serious accident and needs blood transfusion immediately. Which one of the blood groups mentioned below and readily available in the hospital will be safe for transfusion ?

In an emergency when the recipient’s blood group is unknown, O negative (O, Rh–) red cells are used because they lack A and B antigens and the Rh D antigen, minimizing risk of immediate haemolytic reaction from recipient antibodies. Type O red cells can be transfused to recipients of any ABO group, and Rh– units avoid anti‑D reactions in Rh‑ recipients, making O negative the universal red‑cell donor for emergencies [1]. Major transfusion guidelines explicitly recommend issuing O negative red cells when rapid provision is needed and the recipient’s blood type is unknown to prevent life‑threatening incompatibility reactions [2].

Sources

1. [1] https://www.redcrossblood.org/donate-blood/blood-types.html
2. [2] https://www.hematology.org/education/patients/blood-basics/blood-safety-and-matching