Blood and Its Components
What are the components of blood?
Blood is made up of a few different types of cells suspended in fluid called plasma, which contains proteins like clotting factors and other substances. The blood that flows through the body in veins and arteries is called whole blood. Each of the components of whole blood has an important role.
Separation of these components is performed by first treating the blood to prevent clotting and then letting the blood stand. Red blood cells settle to the bottom, while plasma migrates to the top. Using a centrifuge to spin out these components can speed up the process. The plasma is then removed and placed in a sterile bag. It can be used to prepare platelets, plasma, and cryoprecipitate antihemophilic factors, again with the help of a centrifuge to separate out the platelets. Plasma may be pooled with that from other donors and processed further (fractionated) to provide purified plasma proteins, such as albumin, immunoglobulin, and clotting factor concentrates.
Blood components used in transfusion medicine include:
Whole Blood (WB)
Whole blood contains red blood cells for transport of oxygen to tissues, white blood cells for fighting infection, platelets for clotting, and plasma, the fluid part of whole blood. Compatibility testing is required before transfusion of whole blood.
Red Blood Cells (RBCs)
Red blood cells (RBCs) typically make up about 40% of the blood volume. RBCs contain hemoglobin, a protein that binds to oxygen and enables RBCs to carry oxygen from the lungs to the tissues and organs of the body. RBCs are prepared from whole blood by removing the plasma from the collection bag. They may be transfused in the treatment of anemia resulting from, for example, kidney failure, gastrointestinal bleeding, or blood loss during trauma or surgery. Donor red blood cells must be compatible with the recipient's plasma. Compatibility testing is required before transfusion.
Fresh Frozen Plasma (FFP)
Plasma is the fluid portion of blood. It consists of water, fats, sugar, protein and salts. Its main functions are to transport the blood cells throughout the body as well as other substances, such as nutrients, clotting factors, antibodies, and waste products. It helps to maintain blood pressure and the fluid-electrolyte and acid-base balances of the body. Plasma may be transfused to help control bleeding when no coagulation factor-specific concentrate is available.
Fresh frozen plasma (FFP) is prepared from whole blood or apheresis collection and frozen at -18C. Donor FFP must be compatible with the recipient's red blood cells. FFP serves as a source of plasma proteins for patients who are deficient in or have defective plasma proteins. FFP use is indicated in management of:
- Preoperative or bleeding patients who require replacement of multiple plasma coagulation factors
- Patients with massive transfusion who have clinically significant coagulation deficiencies
- Patients on warfarin (an anticoagulant) who are bleeding
- For transfusion or plasma exchange in patients with low or non-functioning platelets (thrombotic thrombocytopenic purpura)
- Management of patients with selected coagulation factor deficiencies for which no specific coagulation concentrates are available
- Management of patients with rare specific plasma protein deficiencies
Plasma, Cryoprecipitate Reduced
Plasma, Cryoprecipitate Reduced is prepared from FFP by a process of rapid freezing, followed by thawing and centrifugation, which removes the cryoprecipitate and yields plasma that is deficient in Factor VIII, von Willebrand factor (vWF), and fibrinogen. Other plasma proteins remain in the same concentration as in FFP and, like FFP, this component must be compatible with the recipient's red blood cells.
Cryoprecipitate antihemophilic factors (AHF) are part of the plasma that contains clotting factors to help control bleeding in people with hemophilia and von Willebrand's disease. It is only used in most places in the U.S. when viral-inactivated concentrates containing Factor VIII and von Willebrand factor are unavailable or, at times, during surgery as a hemostatic preparation (fibrin sealant).
Cryoprecipitated AHF is prepared by thawing FFP and recovering the precipitate. Cryoprecipitated AHF contains coagulation Factor VIII, Factor XIII, fibrinogen, vWF, and fibronectin. Transfusion of cryoprecipitated AHF does not require compatibility testing; all ABO groups are acceptable.
Platelets are tiny fragments of cells that are essential for normal blood clotting. Platelets may be used in the treatment of leukemia and other types of cancer and conditions in which patients have a shortage of platelets (e.g., thrombocytopenia) or abnormal platelet function to control bleeding.
A unit of platelets is a concentrate of platelets separated from a unit of Whole Blood and suspended in a small amount of the original plasma. Platelets may also be collected by apheresis specific for platelets (plateletpheresis). It is preferred that donor platelets be compatible with the recipient’s red blood cells though compatibility testing is not required. All ABO groups are acceptable for transfusion. Platelets are essential for normal hemostasis. Platelet transfusion is indicated for treatment of patients bleeding due to critically decreased circulating platelet count or functionally abnormal platelets.
White Blood Cells (WBCs)
White blood cells (WBCs) are an important part of the body's defense system. They help protect against infections and also have a role in inflammation, allergic responses, and protecting against cancer. One type, called granulocytes, can be transfused to fight infections that are unresponsive to antibiotic therapy, although the effectiveness of this form of treatment is still being investigated.
Factor VIII Concentrate
Factor VIII preparations can be derived from human plasma or produced by recombinant technology. Recombinant Factor VIII is the product of choice for treating hemophilia A because it is derived from hamster cell lines and thought to be very safe in regard to transmitting human infectious organisms. Human plasma-derived Factor VIII concentrate (anti-hemophilic factor, AHF) is prepared by fractionation of pooled human plasma that is frozen soon after phlebotomy. Factor VIII concentrate is indicated for treatment or prevention of bleeding episodes in hemophilia A patients with moderate-to severe congenital Factor VIII deficiency.
Factor IX Concentrates
- Recombinant and plasma-derived Factor IX concentrates are available.
- Recombinant Factor IX is the treatment of choice for new patients with hemophilia B.
- Factor IX concentrates are used for the treatment of patients with Factor IX deficiency, commonly known as hemophilia B.
Albumin and Plasma Protein Fraction
- Albumin is derived from donor plasma obtained from whole blood donation or plasmapheresis (apheresis specific for plasma). It is composed of 96% albumin, 4% globulin and other proteins and is prepared by a cold fractionation process. These products do not transmit viral diseases.
- Plasma Protein Fraction (PPF) is a similar product that contains 83% albumin and 17% globulin.
- Albumin is used in patients whose volume of blood is dangerously low (hypovolemic) and who have low concentrations of proteins in their blood (hypoproteinemic). Indications for PPF are the same.
Immune globulins are preparations of antibodies that protect against certain diseases and are derived from pools of human plasma.
- Gammaglobulin preparations and specific hyperimmune globulin preparations with high titers against specific infectious agents or toxins are available for intramuscular use (IMIG). Intramuscular products are given primarily for disease protection or prophylaxis.
- Intravenous gammaglobulin (IVIG) preparations provide a mechanism to achieve peak levels of IgG immediately after infusion.
- Immune globulin preparations can be used to provide passive antibody prophylaxis for susceptible individuals exposed to certain diseases and a replacement therapy in primary immunodeficiency states.
Synthetic Volume Expanders
Synthetic volume expanders are solutions that are manufactured and are not derived from human blood. When patients do not need the benefits of blood transfusion, such as the oxygen-carrying capacity from red blood cells, but need the volume of their body fluids increased, these solutions may be given intravenously.
- Solutions such as normal saline and Ringer’s Lactate are compatible with plasma. Normal saline contains only sodium and chloride ions, while Ringer’s lactate also contains potassium, calcium and lactate. Solutions such as normal saline and Ringer’s Lactate alone expand the plasma volume temporarily as they rapidly cross capillary membranes.
- Solutions used for volume expansion include Dextran and hydroxyethyl starch (HES). Both Dextran and HES are useful as volume expanders in hemorrhagic shock (shock resulting from extreme blood loss) and the treatment of burns.
Leuko-reduced blood products
This type of component is prepared by removing all or most of the white blood cells (WBCs, leukocytes) from the component. The use of leuko-reduced blood products (red blood cells, platelets) is indicated for patients who have repeated febrile (fever) transfusion reactions. The use of these components has also been shown to reduce the formation of HLA antibodies (antibodies directed against human leukocyte antigens, markers found on WBCs). It also reduces the risk of transfusion-transmissable CMV (cytomegalovirus).
Irradiated blood products
These are blood components that have been exposed to gamma rays or X-rays. This process prevents transfusion-related graft versus host disease (TA-GVHD), a condition in which the white blood cells from the donor produce an immune response against (attack) recipient's cells. Irradiation prevents donor white blood cells from replicating in the recipient and prevents complications from TA-GVHD. Irradiated blood products are indicated for use in patients with compromised immune systems.