Chemical substances found on red blood cells determine blood groups. The two most important blood group systems are the ABO system and the Rhesus[Rh] system. Within the ABO system people can have four types: O, A,B or AB.
Within the Rh system, people can be either Rh positive or Rh negative. Each system is inherited independently of the other and therefore there are eight main groups.
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– Distribution of Blood Groups among blood donors in South Africa
– Compatibility of Blood Groups
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