The Transfusion Medicine laboratory is responsible for the testing and storing of blood products that will eventually be transfused into patients. Many people are familiar with traditional blood transfusions, however, the Transfusion Medicine laboratory carries many other types of blood products that are requested to be transfused into patients, such as platelets, fresh frozen plasma, albumin, etc.
Packed red blood cells are administered to patients that have a severely low hemoglobin or are actively bleeding. One unit of packed cells can increase the patient’s hemoglobin by 10 g/L. In Canada, all blood products are received from Canadian Blood Services (CBS) (or Héma-Québec for residents of Québec). When packed cells are received from CBS, the blood type must be double checked in order to determine whether it is correct. A life-threatening transfusion reaction would occur from a patient being transfused the wrong blood type. When received into the laboratory, these units must be stored at 1-6°C. This temperature requirement changes to 1-10 °C while being transported. There are different ways that packed red blood cells can be prepared to fit the need of the patient. First of all, blood can be “leuko-reduced”, meaning that the white blood cells are removed from the unit. This procedure is done for two main reasons. First, it prevents a non-threatening transfusion reaction known as febrile non-hemolytic transfusion reaction. This transfusion reaction is due to antibodies present in patients’ white blood cells that act against red blood cells. Secondly, this process prevents the transmission of cytomegalovirus (CMV), which is a virus transferred through white blood cells, and can seriously infect immunocompromised patients or babies. Packed cells can also have the option of being washed for those patients that have had previous allergic reactions during transfusions. This washing removes the plasma proteins that cause these allergic reactions during transfusions. Packed cells can also be irradiated, meaning that they have been exposed to gamma irradiation. This prevents transfusion associated graft-versus-host disease, which is a rare complication of transfusions. During this disease, donor lymphocytes are not detected as “non-self” and are not destroyed. Then, the donor lymphocytes create an immune response against the patient’s cells. This transfusion reaction can occur to patients that are immunocompromised, as they cannot destroy these donor lymphocytes. Finally, whenever blood is ready to be transfused into a patient, a label is generated that contains the patient’s name, identification number, blood group, and whether the blood is crossmatch compatible. Along with that is another label on the unit of blood that contains the donor number, expiration date, and blood type of the unit. Before being transfused to the patient, the Transfusion Medicine laboratory issues the unit to a healthcare professional. Most times, blood is immediately transfused into the patient, however, if the unit ends up not being needed, then it must be returned after 30 minutes if it is not in a temperature controlled cooler, and four hours if it is.
Another common product transfused into patients are platelets. This product is given to those who are actively bleeding due to decreased platelets (known as thrombocytopenia), or malfunctioning platelets (known as thrombocytopathies). Platelets are generally transfused whenever a patient’s platelet count is less than 20×109/L. By transfusing just one unit of random-donor platelets, a patient’s platelet count would increase by 5×109/L in one hour for random donor platelets, and 8-10×109/L in one hour for apheresis platelets. Proper storage conditions are in place for platelets as well, as they must be stored at room temperature on an agitator to prevent platelet clumping.
Fresh frozen plasma is also transfused in many patients. Since it contains all stable coagulation factor proteins, as well as normal levels of Factor V and slightly decreased levels of Factor VIII, it is used in the treatment of coagulation factor deficiencies. With vitamin K deficiency due to malnutrition or liver disease, coagulation factors dependent on vitamin K can be decreased, causing excessive bleeding. In addition, whenever a patient has decreased coagulation factors due to disseminated intravascular coagulation (a condition in which severe clotting causes a decrease of coagulation factors), factor deficiencies can occur as well. While this product comes from CBS in a frozen state, before being transfused into a patient, it must be thawed in a 37°C water bath, and transfused within 24 hours. Before being thawed, the product must be stored at either -18°C for one year or less than -65°C for 7 years.
There are other miscellaneous products that are also issued from the Transfusion Medicine laboratory. One of these is intravenous immunoglobulin, which is used to treat patients with immune deficiencies. Another product is albumin. There are two different types of albumin given, depending on the need for the product. For patients experiencing a volume deficit, 5% albumin is given, whereas 25% is given for patients that have a low oncotic pressure.
Finally, another product given to patients, specifically mothers, in the Transfusion Medicine laboratory is Rh immune globulin (RhIg). This product is given to mothers that type as Rh negative, and the product prevents the production of anti-D against the red blood cells of their fetus, known as hemolytic disease of the fetus and newborn. As mentioned in my previous blog, Rh antibodies are not inherently present in the blood, and must have a stimulus to be produced. This stimulus could either have occurred from a previous birth, transfusion, miscarriage, abortion, etc. From the first contact of Rh positive blood, a primary immune response occurs in which memory B cells are created that have a memory of the foreign substance (Rh antigen) present in the body. Therefore, whenever this foreign body is present again, these cells will be quick to produce antibodies. Once the antibodies are transported from the mother’s circulation to the baby through the placenta, antibodies coat the red blood cells and are removed from the fetal circulation by macrophages, causing the child to become anemic. If anemia in the child is severe, hydrops fetalis can occur, possibly causing death of the fetus. Hemolysis from the cells also releases bilirubin, which is toxic to babies as they cannot metabolize it due to lacking the enzyme glucoronyl transferase, which breaks it down. The indirect bilirubin accumulates in the brain causing kernicterus, which leads to brain damage. To prevent this from happening, RhIg is given. RhIg is an immunoglobulin that attaches to any Rh positive red blood cells present in the mother’s circulation before she is sensitized to produce any antibodies. Then, the spleen removes the antibody coated cells from the circulation, and does not initiate an immune response against the cells. RhIg is given twice during a pregnancy, first at 28 weeks of gestation, and again 72 hours after delivery.