BLOOD AND BLOOD PRODUCTS FOR TRANSFUSION
The role of the biomedical scientist in the transfusion laboratory is to ensure that the blood and blood products being transfused into a patient are safe. To ensure safety, the blood is tested to determine its blood group and to check that it is not contaminated with harmful microorganisms. In addition, checks are made to ensure that the transfused blood does not contain anti-bodies that will destroy the erythrocytes of the recipient and cause death.
Blood transfusions are required to replace blood lost as a result of accident or surgery. Surgical procedures which require transfusions include the trans-plantation of organs, such as the liver and heart, where significant bleeding may occur. Blood may also be given to treat certain diseases, such as anemia. Plasma may also be transfused to treat badly burned patients who have lost significant amounts of fluid or in the treatment of bleeding disorders. Plasma products, such as Factor VIII, to treat hemophilia , or immu-noglobulins, to treat certain immunodeficiency disorders , may also be given. Platelet concentrates are also used to treat bleeding disorders (Figure 6.1).
In the UK, blood containing leukocytes is no longer transfused for a number of reasons, as shown in Table 6.1. Sensitization to Major Histocompatibility Complex (MHC) antigens, which are present on blood leukocytes but not erythrocytes, may have consequences if the recipient later requires a trans-plant and GVHD may have a fatal outcome in immunosup-pressed individuals. As a consequence, leukocytes are removed from blood, usually within a few hours of collection. This involves filtering the blood through leukocyte-specific filters, which trap the leukocytes but not the smaller erythrocytes or platelets. Such a process is called leukodepletionand it reduces the leukocyte count to less than 5 q 106 dm –3. The number of leu-kocytes left in blood can be assessed by counting in a hemocytometer, or by using a flow cytometer.