What is the rarest blood type: A, B, or AB?

Our blood types are determined by specific markers, called antigens, found on the surface of our red blood cells. The ABO system is the most well-known classification, identifying individuals as having A antigens, B antigens, both A and B antigens, or neither. These antigens are crucial because they dictate which blood types can be safely mixed during transfusions, preventing potentially life-threatening immune reactions.

The type that possesses both A and B antigens is indeed the rarest among the primary ABO blood groups. This particular blood type arises when an individual inherits an A allele from one parent and a B allele from the other. Since both A and B are codominant alleles, they are both fully expressed, resulting in the presence of both antigen types on the red blood cells. This specific genetic combination occurs less frequently in the general population compared to inheriting two A alleles, two B alleles, or any combination involving the O allele, which is recessive.

Globally, only about 1-4% of people have this distinct blood type, making it significantly less common than A, B, or O. Its unique characteristic of having both A and B antigens makes these individuals "universal recipients" for red blood cell transfusions within the ABO system, as their immune system recognizes both A and B as "self." This rare blood type highlights the fascinating diversity and complexity within human biology, underscoring why understanding blood groups is vital for medical science and patient care.