Rh Incompatibility - Essay Example

Rh Incompatibility The Rh system is, perhaps, the most important blood group system in human blood in the context of clinical implications. This is a mandatory parameter in pretransfusion testing. The Rh antigens are found as a part of red blood cell membrane protein. Since there are about 40 different antigens recognised in this group, these are known as Rh system. Out of these, only 5 types are known to occur frequently, and these are termed as D antigens. Thus, if D antigen is present on the red blood cells, the blood is known as Rh positive, and absence of D antigen confers Rh negativity.

The D antigen is a potent alloantigen, meaning this can result in production of antibodies quickly on exposure. Considering the fact that 15% population who lacks D antigen, if these Rh-negative people are exposed to even a minute quantity of Rh-positive cells, by either pregnancy or transfusion, these subjects will immediately develop anti-Rh antibody. Thus this incompatibility would lead to production of an alloantibody in the subject's blood. These antibodies are usually of the class immunoglobulin G or IgG.

These antibodies commonly bind to the antigens located on the surface of red blood cells. This could initiate a reaction that may end up in hemolysis of the red blood cells. IgG antibodies can cross placenta and bind fetal erythrocytes that bind with corresponding antigens. This leads to hemolysis of the fetal red blood cells, commonly known as hydrops fetalis, which is a severe manifestation of hemolytic disease of the newborn. Due to these reasons, all pregnant women and potential donors and recipients of blood are tested for blood groups and antigens, specifically Rh antigen.

The Rh antigen is tested using reagent antisera directed against Rh antigens. Despite these, adverse reactions may result from incompatibility. Most frequent clinical occurrences of Rh incompatibility occurs when a mother is Rh negative and the father is Rh positive. Taking this example, the developing fetus has equal chances of being Rh positive or Rh negative. In the case where the fetus is Rh positive in contrast to the mother being Rh negative, even a small quantity of fetal blood passing into the mother's circulation will generate antibody against fetal Rh antigens in the mother's blood.

This kind of autotransfusion is a frequent phenomenon throughout the period of pregnancy. This results in sensitization of fetal blood against mother's blood and will lead to generation of IgG antibodies against fetal Rh antigen's in the mother's blood. Since the mother is Rh negative, this would lead to no effects in the mother's circulation; whereas, in the next situation, if these IgG antibodies enter the fetal circulation from that of the mother, it will lead to a hemolytic process in the fetal blood.

This fetus may be born with hemolytic disease of the newborn. This is almost similar to the phenomenon of accidental or erroneous transfusion reaction that occurs when Rh-negative blood is transfused to Rh-positive individuals. Since the main pathologic phenomenon is hemolysis, this clinically may take the form of hypotension, tachycardia, fever, chills, hemoglobinemia, hemoglobinuria, chest pain, flank pain, discomfort at the transfusion site in the adult individuals. While the fetus in utero does not show such clinical signs, intravascular hemolysis and hemoglobinemia would lead to excessive hemoglobin deposition in the amniotic fluid surrounding the fetus.

This can be assessed in the laboratory by analysis of the amniotic fluid, and untreated, the baby will have severe jaundice and swelling of the body due to decreased blood volume. A catastrophic incident like this can be detected in accidental adult transfusion by measurement of haptoglobin, lactate dehydrogenase, and indirect bilirubin. Same is the case with hemolytic disease of the newborn where all these parameters are elevated in the fetus, newborn, or amniotic fluid. Prevention of such an event in adult transfusion is done by extreme caution and care to do a pretransfusion testing and almost intensive surveillance at the time of transfusion.

In case of the fetus, all mothers will Rh negative blood should receive passive immunization with anti-D to reduce or prevent sensitization especially after the first pregnancy or abortion.