blood group

the division and classification of people into one of four main groups based on the presence of ANTIGENS on the surface of the red blood cells (corpuscles). The classifying reaction depends on the SERUM of one person's blood agglutinating (clumping together) the red blood cells of someone else. The antigens, known as agglutinogens, react with antibodies (agglutinins) in the serum. There are two agglutinogens termed A and B and two agglutinins called anti-A and anti-B. This gives rise to four groups: corpuscles with no agglutinogens, group O; with A; with B; with both A and B (hence blood group AB). The agglutinin groups match those of the agglutinogens. thus a person of blood group B has anti-A serum in his or her blood. It is vital that blood groups are matched for transfusion because incompatibility will produce blood clotting. The rhesus factor or Rh factor is another antigen (named after the rhesus monkey, which has a similar antigen), those with it being Rh-positive and those without Rh-negative. About 85 percent of people are Rh-positive. If a Rh-negative person receives Rh-positive blood, or if a Rh-positive foetus is exposed to anti- bodies to the factor in the blood of the Rh-negative mother, then HAEMOLYSIS occurs in the foetus and newborn child. This may cause the stillbirth of the child or jaundice after birth. Testing of pregnant women is thus essential.