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The O-positive blood type is not a rare blood type. It is the most common blood type, according to the American Red Cross. The rarest blood type is AB negative.


AB negative is the rarest blood type. On average, about 5 percent of the population is AB negative. There are four major types of blood: A, B, AB and O.


Of the eight different common blood types, AB negative is the least common blood type in the United States, according to the American Red Cross. O positive is the most common type, followed by A positive as the second most common, and then B positive.


The blood types and their global prevalence are A+ at 28.3 percent, A- at 3.5 percent, B+ at 20.6 percent, B- at 1.4 percent, AB+ at 5.1 percent, AB- at 0.5 percent, O+ at 36.4 percent and O- at 4.3 percent. The rarity of each type varies greatly by region.


Blood types from the most common to rare are O +, A +, B +, O -, A -, AB +, B - and AB -. Each type is determined by the presence or absence of certain antigens on the surface of the blood cells.


A list of the rarest blood types is maintained online at KnowYourBlood.com. As of 2015, information detailing rare blood types can also be found on the websites of the American Red Cross and New Health Guide.


The American Pregnancy Association explains that the presence or lack of the Rh factor determines whether a blood type is positive or negative. The Rh factor is an antigen and a protein type located on the surface of red blood cells that causes an immune system response...