Blood groups

The ability to withdraw, store and then transfuse blood safely has been a major advance this century, saving thousands of lives and allowing major surgery to be performed. The understanding of blood groups made this possible. The pioneering researcher in this field was Karl Landsteiner (1868-1943), the Austrian scientist and Nobel Prize winner. At least ten blood group systems have now been identified but only two are of importance in the vast majority of cases: the ABO system, and the rhesus system (so called because much of the early research was performed on blood from rhesus monkeys). Each red cell has various antigens built into its outer membrane. The type of antigen depends on inherited genes. The ABO blood groups refer to the presence or absence of a certain pair of antigens on every red cell. Group A people have red cells with antigen A only; group B have B antigens; group AB have both; and group O have neither. Each person also has antibodies in their blood to the antigen or antigens not present on their red cells; so group A people have an antibody to B, group O will have both A and B antibodies, and soon.

The presence of these antibodies means that if blood with antigen A (group A) was transfused to a person with antibody A (group B or O) a reaction would occur and the transfused blood would be destroyed. This not only renders the transfusion pointless but can also lead to serious complications, with damaged red blood cells sticking together in clumps and blocking blood vessels.

Those people in group O, therefore, can donate their blood to anyone because there are no anitgens present; they are ‘universal donors’. Group AB people are ‘universal recipients’ in that they can receive blood from anyone because they have neither antibody A nor B in their blood. However this concept of ‘universality’ can be a dangerous assumption as incompatibility may still occur. Therefore, unless there is a serious emergency, only blood of the same group will be used for transfusion and only after mixing blood samples has shown that coagulation of blood cells does not occur.

The rhesus blood group refers to the presence or absence of an antigen called the rhesus factor. The rhesus factor is particularly important when it comes to pregnancy and is one reason for the blood test advised after conceiving. If a rhesus negative mother has a rhesus positive partner their child may be rhesus positive, that is, have the rhesus antigen. The mother’s blood can, under certain condition, destroy the baby’s blood and the baby may be born severely ill with anaemia and jaundice. This situation, called rhesus incompatibility or haemolytic disease of the newborn, occurs in about one baby in 200. This problem has been largely overcome in the developed world by immunization.