What is the rarest blood type?

Our blood is categorized into different types based on the presence or absence of specific antigens on the surface of red blood cells. The two main systems for classification are the ABO system, which identifies A, B, AB, or O types, and the Rh system, which determines whether blood is positive (+) or negative (-). The combination of these two systems gives us the eight primary blood types. Among these, the type that occurs least frequently in the population is AB negative.

AB negative blood is notably rare because it requires a unique genetic inheritance. Individuals with AB blood have both A and B antigens on their red blood cells, which is less common than having only A, only B, or neither (O). To be AB negative, a person must also lack the Rh factor, another antigen, which is present in the majority of people. This specific combination of genes makes AB negative blood found in less than one percent of the population, making it the rarest of the common blood types.

The scarcity of AB negative blood makes donations incredibly important. While people with AB negative blood can only receive red blood cells from other Rh-negative types (AB-, A-, B-, or O-), they are considered universal plasma donors. This means their plasma, which contains no A or B antibodies, can be given to patients of any blood type in emergencies. This unique characteristic highlights the critical role that individuals with this rare blood type play in transfusion medicine.