10.5 - Blood Groups of Humans

ABO Blood Group

Human blood group can be classified into 4 – A, B, AB and O blood groups. Knowing your blood type is important because when it comes to having a blood donation or transfusion. Incompatible blood groups will result agglutination which is fatal.

The surface antigens on the surface of the erythrocytes determine what type of blood group you have.

• Blood groups A

  • Antigens on the red blood cells: Antigen A
  • Antibody in the plasma: Antibody B

• Blood groups B

  • Antigens on the red blood cells: Antigen B
  • Antibody in the plasma: Antibody A

• Blood groups AB

  • Antigens on the red blood cells: Antigen A and antigen B
  • Antibody in the plasma: No

• Blood groups O

  • Antigens on the red blood cells: No
  • Antibody in the plasma: Antibody A and antibody B

Only compatible blood groups can donate or receive one another.

• Blood groups A

  • Can donate blood to A and AB only
  • Can receive blood from A and O only

• Blood groups B

  • Can donate blood to B and AB only
  • Can receive blood from B and O only

• Blood groups AB

  • Can donate blood to AB only
  • Can receive blood from all blood groups

• Blood groups O

  • Can donate blood to all blood groups
  • Can receive blood from O only

Rhesus Factor

Rhesus factor , or Rh factor, is another type of antigen (antigen D) found on the surface of the red blood cells. This antigen is genetically-inherited, which means if you have the antigen, you are Rh-positive. Meanwhile, if you do not have the antigen, you are Rh-negative.

If a Rh-positive blood is mixed with a Rh-negative blood, the incompatibility will trigger the production of Rhesus antibody or anti-D antibody. This condition can be lethal if it happens during pregnancy.

Figure 15 - It becomes a problem when the mother, who is Rh-negative conceives a Rh-positive fetus. The presence antigen D in the fetal blood cells will trigger the production of anti-D antibodies in the mother's blood. The antibodies are able to diffuse into the fetal blood system through the placenta. The antibodies are able to destroy the fetal erythrocytes before or immediately after birth. However, the amount of the antibodies is not sufficient to affect the baby. The antibodies remain in the maternal blood system. When the mother conceives a second child who is also Rh-positive, the anti-D antibodies will cross the placenta and destroy the fetal erythrocytes. This condition is called erythroblastosis fetalis. The second fetus can die if his/her blood is not replaced with a Rh-negative blood. In less severe condition, the baby can suffer from anemia and mental retardation. This problem can be overcome by treating the mother with anti-Rh globulins to inhibit the formation of anti-D antibodies.