39% of the population
O+ blood has no A or B antigens, and is thus “O” blood. The (+) means that the Rh antigen is present.
O+ blood is very important as a (mostly) universal red blood cell type. This blood type can be used in emergency situations such as traumatic bleeding or other types of emergency transfusions. It is also an important blood type as type “O” patients can only receive type “O” red blood cell transfusions. It cannot be used in all situations as it does have the Rh antigen present – but it is becoming more widely used in emergency situations and is often one of the most needed red blood cell donations. O+ donors are encouraged to donate whole blood and apheresis red blood cells.