ABO Blood Groups and Rho Types
Blood groups and types can make for a very complex discussion, but the basic design can be easily presented. There are many structures on the surface of a red blood cell much like landscape of a city. Some are simple houses while other are big buildings with basement parking garages. Here we will just focus on a well known and easy to understand neighborhood of these cell structures called the ABO and Rho system.
Group and Type
A red blood cell (RBC) is grouped and typed by the formation of structures (Antigens) on the surface of the red blood cell. These formations are made of protein and amino acid structures that are also found throughout the body. Like a doorman at the night club checking ID cards, it is these different variations of antigens that is specific for each person that helps the immune system to identify objects within the body as self or not self. Your immune system is constantly checking the ID cards of the objects in your blood stream, protecting you against invaders. The ABO antigens are what provides you a blood GROUP and the Rho antigens provides you with a blood TYPE. These are the two main indentifiers, Group & Type, used to provide compatible blood products for our patients.
Group O Rho- (D negative) RBC is without any ABO and Rho antigens. Only 7% of the population have this group and type. It’s lack of ABO and Rho antigens that makes it the group and type of choice for emergency transfusion situations.
Group O Rho+ (D positive) RBC is without any ABO structures but displays the Rho antigen. With 38% of the population having this group and type it is the most common.
Group A Rho- (D negative) RBC displays the A antigen but does not display the Rho antigen. Only 6% of the population have this group and type.
Group A Rho+ (D positive) RBC displays both the A and the Rho antigen. With 34% of the population having this group and type, it is the second most common.
Group B Rho- (D negative) RBC displays the B antigen but not the Rho antigen. With only 2% of the population having this group and type, it is the second least common; and is in high demand by hospital blood suppliers since B neg patients can only receive B neg and O neg red blood cell products.
Group B Rho+ (D positive) RBC displays both the B and the Rho antigen. Only 9% of the population have this group and type.
Group AB Rho- (D negative) RBC displays both A and B antigens but not the Rho antigen. With only 1% of the population having this group and type, that makes it the least common group and type. However this blood group lack ABO antibodies allowing them to recieve red cell products from any blood group as long as the Rh type is Rho- (D negative).
Group AB Rho+ (D positive) RBC displays both A and B antigen as well as the Rho antigen. Only 3% of the population have this group and type. With having all possible ABO and Rho antigens, people of this group and type lack ABO and Rho antibodies allowing them to recieve any group and type of red cell product.
Antigen vs. Antibody
Antibodies are produced by the immune system to label invaders for destruction. Antibodies are very specific to what they attach themselves to. The structure that an Antibody attaches to is called an Antigen. Antigens are also what helps the immune system distinguish between self and non-self. So when the immune system comes in contact with an unknown antigen that is non-self, it will label that antigen for destruction with a antibody specific to only that antigen. This process is important to remember when transfusing blood products to a patient, because blood that is not compatible with the immune system of the patient could have disasterous results.
The Rho antigen system is large and complex in structure and the immune system will develop specific antibodies to the Rho antigen by exposure to this antigen. However the ABO system is different. The antibodies to the ABO antigen system are developed naturally through constant exposure beginning at birth and start to appear at four months of age. The rule of thumb is that the body will only make an antibody to antigens that body does not have. Therefore Group A people will not develop Group A antibodies; they will however develop Group B antibodies for protection. Interestingly enough the body will not make an antibody to Group O blood since there is no O antigen. Group O blood is just red blood cells that do not have the A or B antigen.
Blood Transfusion can be a dangerous undertaking. Besides the risk of disease transmission, there are many other antigen antibody interactions that could cause problems. Most of the other antigen antibody interactions require some previous exposure to that specific RBC antigen to generate an immune response creating that specific antibody. The Rho antigen is almost a sure thing to cause an immune response when exposed to an Rho- (D negative) person. So with that in mind we transfuse Rho+/- appropriately. The Good thing about blood transfusion is that with modern disease testing and screening techniques, it is thought that blood products today are more safe now than ever before.
|O neg||O neg|
|O pos||O pos||O neg|
|A neg||O neg||A neg|
|A pos||O pos||O neg||A pos||A neg|
|B neg||O neg||B neg|
|B pos||O pos||O neg||B pos||B neg|
|AB neg||O neg||A neg||B neg||AB neg|
|AB pos||O pos||O neg||A pos||A neg||B pos||B neg||AB pos||AB neg|
|Unknown||O neg||O pos *|