Answer:
Type O is often called the 'universal donor' because these red blood cells don't have antigens. This type, specifically type O negative (which is the true 'universal donor'), is the most valuable because it can be administered to virtually everyone. That's why it's often carried on medical helicopters.
Why is O blood valued by the Red Cross?
Type O positive blood is given to patients more than any other blood type, which is why it's considered the most needed blood type. 38% of the population has O positive blood, making it the most common blood type.
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