Sunday, May 1, 2011

Blood Typing

After taking the assessment test, I realized I needed to brush up on blood typing. It is a fairly easy subject but everyone needs a refresher, right?

There are two major players when it comes to blood typing: antigens and antibodies. Antigens reside on the surface of the blood cell and are of three possible types: antigen A, antigen B, and Rh antigen. Antibodies are present in the blood plasma and appear in the first part of a persons life in response to environmental factors. There are two types of these immunoglobins: Anti-A and Anti-B antibodies.

There are two systems of blood-grouping: The ABO system and the Rh system. The ABO system is better recognized and understood, but the Rh system is quite different. When a person's blood is tested they are given one of the following designations: A, B, AB, or O which signifies which (if any) antigens are present on the surface of their RBCs. A (-) or (+) is then placed after the letter(s) to indicate the absence (-) or presence (+) of the Rh antigen on their cells. These designations are important when it comes to blood transfusions and pregnancy.

For instance, if a patient receives a blood transfusion from someone whose blood type differs from their own, agglutination of the cells may occur. Agglutination of the red blood cells is a state where the cells literally clump together resulting in an adverse effect in the individual. This agglutination is in response to the Anti-A antibodies binding with the A antigens and Anti-B antibodies binding with the B antigens on the cells. However, with type-O blood, there are no antigens present on the cells, thus, when Anti-AB serum is added to the blood no agglutination occurs. Traditionally, it is understood that type O- individuals are universal donors because their RBCs contain no antigens and type AB+ individuals are universal recipients because they have all possible antigens on the surface of their cells.

As mentioned earlier, the Rh factor of blood is exceedingly important during pregnancy. A pregnant, Rh- woman carrying a Rh+ fetus can begin to develop Rh antibodies if some of the fetus's blood crosses the placental barrier and enters the mothers bloodstream (in the case of a fetomaternal hemorrhage during childbirth). This switching from Rh- to Rh+ may cause the mother to develop Rh disease. Additionally, if a Rh- mother becomes Rh+ after her first pregnancy and later carries a fetus with Rh- blood and the mothers blood crosses the barrier, hemolytic disease of the newborn may occur.