Introduction to Blood Transfusions
Basic Information About Blood Products and Blood Typing
Jan 3, 2009
Blood transfusions are a significant medical advancement. The ability to transfer blood components from one person to another has saved countless lives. It is also a therapy that requires careful preparation and pretreatment testing to minimize the risks and complications.
The following information is an overview of blood transfusions, specifically the types of blood transfusions and the methods of blood typing.
Types of Blood Products
Blood consists of a liquid component (plasma) and a cellular component. Different contents of a donor's blood can be purified and given to a recipient who needs them. Type of blood products that can be transfused include the following:
- Red Blood Cells (RBCs): Transfusion of RBCs is helpful for patients with a significantly lower blood hemoglobin level than usual. Each unit of RBCs raises the blood hemoglobin level by 1 gram per deciliter (g/dL).
- White Blood Cells (WBCs): For patients with very low WBC counts, transfusion of these cells can be an option. However, this type of transfusion is rarely performed.
- Platelets:Platelets are transfused when the blood platelet count is less than 10,000 cells per microliter for patients without symptoms or less than 50,000 cells per microliter for patients with symptoms. One unit of platelets increases the blood platelet level by 10,000 cells per microliter.
- Fresh Frozen Plasma (FFP): FFP is transfused when a patient has major depletion of multiple clotting factors. Clinical indications include but are not limited to overuse of warfarin and disseminated intravascular coagulation.
- Cryoprecipitate:Cryoprecipitate consists of concentrated clotting factors VIII and XIII plus fibronectin and von Willebrand factor. This is generally useful for deficiencies of these specific clotting factors.
All donor blood is tested for infectious agents and antibodies to certain blood components. In addition, RBC transfusions require donor and recipient blood to be typed for compatibility. There are two widely used systems of blood typing: ABO and Rh.
ABO Typing
The ABO system characterizes RBCs as follows:
- Type A blood has RBCs with the A antigen.
- Type B blood has RBCs with the B antigen.
- Type AB blood has RBCs with both A and B antigens.
- Type O blood has RBCs with neither the A nor the B antigen.
When an RBC antigen is absent, the plasma has antibodies to that missing antigen, as described below:
- Type A blood has anti-B antibodies.
- Type B blood has anti-A antibodies.
- Type AB blood has neither anti-A nor anti-B antibodies.
- Type O blood has both anti-A and anti-B antibodies.
Transfusion of RBCs involve the introduction of donor RBCs into the recipient's plasma. It must be done so that the recipient's antibodies do not attack the RBCs, as described next:
- Type A individuals can receive RBCs of type A or O.
- Type B individuals can receive RBCs of type B or O.
- Type AB individuals can receive RBCs of any type ("universal recipient").
- Type O individuals can only receive RBCs of type O, but they can donate their RBCs to anyone ("universal donor").
Rh Typing
In addition to ABO typing, RBCs are classified by the Rh system. Rh-positive blood has RBCs with the D antigen and no Rh antibodies in the plasma, whereas Rh-negative blood has RBCs without the D antigen and Rh antibodies present in the plasma. Rh-positive individuals can receive Rh-positive or Rh-negative RBCs, but Rh-negative individuals should only receive Rh-negative RBCs.
Blood Transfusions a Valuable Lifesaver
A variety of complications can still result from blood type mismatching, the presence of certain antibodies, infectious agents, and other factors, all of which are beyond the scope here. However, if the whole process is performed carefully, blood transfusion can still be a valuable lifesaver.
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