AEMCA Practice Exam

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Which blood group is known as the universal donor?

AB-
O+
O-
B-

The correct answer is: O-

The universal donor blood group is O-. This designation comes from the absence of A and B antigens on the surface of the red blood cells of O- blood. This means that O- blood can be transfused to patients of any blood type without the risk of an immune response triggered by incompatible blood antigens. In transfusions, the presence of A and B antigens can cause serious transfusion reactions if the recipient's blood contains antibodies against those antigens. Since O- blood lacks these antigens, it can safely be given to individuals with any of the other blood types (A, B, AB, or O) irrespective of Rh factor. This feature makes O- particularly critical in emergency situations where blood type might not be immediately known. In contrast, other blood types may have specific antigens that can lead to complications in transfusions, making O- unique as the safest choice for universal donation.