Transfusion is the process of transferring whole blood or blood components from a donor to a recipient.
Transfusions are given to restore lost blood, to improve clotting time, and to improve the ability of the blood to deliver oxygen to the body's tissues. About 32,000 pints of donated blood are transfused each day in the United States.
In the United States, blood collection is strictly regulated by the Food and Drug Administration (FDA). The FDA has rules for the collection, processing, storage, and transportation of blood and blood products. In addition, the American Red Cross, the American Association of Blood Banks (AABB), and most states have specific rules for the collection and processing of blood. The main purpose of regulation is to ensure the quality of transfused blood and to prevent the transmission of infectious diseases through donated blood. Before blood and blood products are used, they are extensively tested for such infectious agents as hepatitis and human immunodeficiency virus (HIV).
Either whole blood or its components can be used for transfusion. Most blood collected from donors is broken down (fractionated) into components that are used to treat specific problems or diseases. Treating patients with fractionated blood is the most efficient way to use the blood supply.
WHOLE BLOOD. Whole blood is used exactly as received from the donor. Blood components are parts of whole blood, such as red blood cells (RBCs), white blood cells (WBCs), plasma, platelets, clotting factors, and immunoglobulins. Whole blood is used only when needed or when fractionated components are not available, because too much whole blood can raise the recipient's blood pressure. Use of blood components is a more efficient way to use the blood supply, because blood that has been fractionated can be used to treat more than one person.
Whole blood is generally used when a person has lost a large amount of blood. Such blood loss can be caused by injury or surgical procedures. Whole blood is given to help restore the blood volume, which is essential for maintaining blood pressure. It is also given to ensure that the body's tissues are receiving enough oxygen. Whole blood is occasionally given when a required blood fraction is unavailable in isolated form.
RED BLOOD CELLS. Red blood cells (RBCs) carry oxygen throughout the body. They pick up oxygen as they pass through the lungs and give up oxygen to the other tissues of the body as they are pumped through the arteries and veins. When patients do not have enough RBCs to properly oxygenate their bodies, they can be given a transfusion with RBCs obtained from donors. This type of transfusion will increase the amount of oxygen carried to the tissues of the body. RBCs are recovered from whole blood after donation. They are then typed, removed from the watery blood plasma to minimize their volume (packed), and stored. RBCs are given to people with anemia (including thalassemia), whose bone marrow does not make enough RBCs, or who have other conditions that decrease the number of RBCs in the blood. Occasionally, red blood cells from rare blood types are frozen. Once frozen, RBCs can survive for as long as ten years. Packed RBCs are given in the same manner as whole blood.
WHITE BLOOD CELLS. White blood cells (WBCs) are another infection-fighting blood component. On rare occasions, white blood cells are given by transfusion to treat life-threatening infections. Such transfusions are given when the WBC count is very low or when the patient's WBCs are not functioning normally. Most of the time, however, antibiotics are used in these cases.
PLASMA. Plasma is the clear yellowish liquid portion of blood. It contains many useful proteins, especially clotting factors and immunoglobulins. After plasma or plasma factors are processed, they are usually frozen. Some plasma fractions are freeze-dried. These fractions include clotting factors I through XIII. Some people have an inherited disorder in which the body produces too little of the clotting factors VIII (hemophilia A) or IX (hemophilia B). Transfusions of these clotting factors help to stop bleeding in people with hemophilia. Frozen plasma must be thawed before it is used; freeze-dried plasma must be mixed with liquid (reconstituted). In both cases, these blood fractions are usually small in volume and can be injected with a syringe and needle .
PLATELETS. Platelets are small disk-shaped structures in the blood that are essential for clotting. People who do not have enough platelets (a condition called thrombocytopenia) have bleeding problems. People who have lymphoma or leukemia and people who are receiving cancer therapy do not make enough platelets. Platelets have a very short shelf life; they must be used within 5 days of blood donation. After a unit of blood has been donated and processed, the platelets in it are packed into bags. A platelet transfusion is given in the same manner as whole blood.
IMMUNOGLOBULINS. Immunoglobulins are the infection-fighting fractions in blood plasma. They are also known as gamma globulin, antibodies, and immune sera. Immunoglobulins are given to people who have difficulty fighting infections, especially people whose immune systems have been depressed by such diseases as AIDS. Immunoglobulins are also used to prevent tetanus after a cut has been contaminated; to treat animal bites when rabies is suspected; or to treat severe childhood diseases. Generally, the volume of immunoglobulins used is small, and it can be injected.
In order to donate blood, an individual must be at least 17 years old, weigh at least 110 lb (50 kg), and be in generally good health. The average blood donor is a white, married, college-educated male between the ages of 30 and 50. Twenty-five percent of people receiving blood transfusions are over the age of 65, although the elderly constitute only 13% of the population. Fewer than 5% of Americans donate blood each year.
Blood is collected from the donor by inserting a large needle into a vein in the arm, usually one of the larger veins near the inside of the elbow. A tourniquet is placed on the upper arm to increase the pressure in the arm veins, which makes them swell and become more accessible. Once the nurse or technician has identified a suitable vein, she or he sterilizes the area where the needle will be inserted by scrubbing the skin with a soap solution or an antiseptic that contains iodine. Sometimes both solutions are used. The donor lies on a bed or cot during the procedure, which usually takes between 10 and 20 minutes. Generally, an 18-gauge needle is used. This size of needle fits easily into the veins and yet is large enough to allow blood to flow easily. Human blood will sometimes clot in a smaller needle and stop flowing. The donor's blood is collected in a sterile plastic bag that holds one pint (450 ml). The bags contain an anticoagulant to prevent clotting and preservatives to keep the blood cells alive. A sample of the donator's blood is collected at the time of donation and tested for infectious diseases. The blood is not used until the test results confirm that it is safe. Properly handled and refrigerated, whole blood can last for 42 days.
The recipient of a transfusion is prepared in much the same way as the blood donor. The site for the needle insertion is carefully washed with a soap-based solution followed by an antiseptic containing iodine. The skin is then dried and the transfusion needle inserted into the vein. During the early stages of a transfusion, the recipient is monitored closely to detect any adverse reactions. If no signs of adverse reaction are evident, the patient is monitored occasionally for the duration of the transfusion period. Upon completion of the transfusion, a compress is placed over the needle insertion site to prevent extensive bleeding.
All donated blood is typed, which means that it is analyzed to determine which of several major and minor blood types (also called blood groups) it belongs to. Blood types are genetically determined. The major types are classified by the ABO system. This system groups blood with reference to two substances in the red blood cells called antigen A and antigen B. The four ABO blood types are A, B, AB, and O. Type A blood has the A antigen, type B has the B antigen, type AB has both, and type O has neither. These four types of blood are further classified by the Rh factor. The Rh, or rhesus factor, is also an antigen in the red blood cells. A person who has the Rh factor is Rh positive; a person who does not have the factor is Rh negative. If a person has red blood cells with both the B and the Rh antigens, that person is said to have a B positive (B+) blood type. Blood types determine which kinds of donated blood a patient can receive. Generally, patients are limited to receiving only blood of the exact same ABO and Rh type as their own. For example, a person with B+ blood can receive blood or blood cells only from another person with B+ blood. An exception is blood type O. Individuals with type O blood are called universal donors, because people of all blood types can accept their blood.
Blood can also be typed with reference to several other minor antigens, such as Kell, Kidd, Duffy, and Lewis. These minor antigens can become important when a patient has received many transfusions. These patients tend to build up an immune response to the minor blood groups that do not match their own. They may have an adverse reaction upon receiving a transfusion with a mismatched minor blood group. A third group of antigens that may cause a reaction are residues from the donor's plasma attached to the RBCs. To eliminate this problem, the RBCs are rinsed to remove plasma residues. These rinsed cells are called washed RBCs.
Autologous transfusion is a procedure in which patients donate blood for their own use. Patients who are to undergo surgical procedures requiring a blood transfusion may choose to donate several units of blood ahead of time. The blood is stored at the hospital for the patient's exclusive use. Autologous donation assures that the blood type is an exact match. It also assures that no infection will be transmitted through the blood transfusion. Autologous donation accounts for 5% of blood use in the United States each year.
Directed donors are family or friends of the patient who needs a transfusion. Some people think that family and friends provide a safer source of blood than the general blood supply. Studies do not show that directed donor blood is any safer. Blood that is not used for the identified patient becomes part of the general blood supply.
Apheresis is a special procedure in which only certain specific components of a donor's blood are collected. The remaining blood fractions are returned to the donor. A special blood-processing instrument is used in apheresis. It fractionates the blood, saves the desired component, and pumps all the other components back into the donor. Because donors give only part of their blood, they can donate more frequently. For example, people can give almost ten times as many platelets by apheresis as they could give by donating whole blood. The donation process takes about one to two hours.
The first step in blood donation is the taking of the donor's medical history. Blood donors are questioned about their general health, their lifestyle, and any medical conditions that might disqualify them. These conditions include hepatitis, AIDS, cancer, heart disease, asthma, malaria, bleeding disorders, and high blood pressure. Screening prevents people from donating who might transmit diseases or whose medical condition would place them at risk if they donated blood. Some geographical areas or communities have a high rate of hepatitis or AIDS. Blood collection in most of these areas has been discontinued indefinitely.
The blood pressure, temperature, and pulse of donors are taken to ensure that they are physically able to donate blood. One pint (450 mL) of blood is usually withdrawn, although it is possible to donate smaller amounts. The average adult male has 10–12 pints of blood in his body; the average adult female has 8–9 pints in hers. Within hours after donating, most people's bodies have replaced the fluid lost with the donated blood, which brings their blood volume back to normal. Replacement of the blood cells and platelets, however, can take several weeks. Pregnant women and people with low blood pressure or anemia should not donate blood or should limit the amount of blood they give. Generally, people are allowed to donate blood only once every two months. This restriction ensures the health of the donor and discourages people from selling their blood. The former practice of paying donors for blood has essentially stopped. Donors who sell blood tend to be at high risk for the transmission of bloodborne diseases.
Recipients of blood transfusion are monitored during and after the transfusion for signs of an adverse reaction. Blood donors are generally given fluids and light refreshments to prevent such possible side effects as dizziness and nausea. They are also asked to remain in the donation area for 15–20 minutes after giving blood to make sure that they are not likely to faint when they leave.
For donors, the process of giving blood is very safe. Only sterile equipment is used and there is no chance of catching an infection from the equipment. There is a slight chance of infection at the puncture site if the skin is not properly washed before the collection needle is inserted. Some donors feel lightheaded when they sit up or stand for the first time after donating. Occasionally, a donor will faint. Donors are encouraged to drink plenty of liquids to replace the fluid lost with the donated blood. It is important to maintain the fluid volume of the blood so that the blood pressure will remain stable. Strenuous exercise should be avoided for the rest of the day. It is normal to feel some soreness or to find a small bluish bruise at the site of the needle insertion. Most donors have very slight symptoms or no symptoms at all after giving blood.
A number of precautions must be taken for transfusion recipients. Donated blood must be matched with the recipient's blood type, as incompatible blood types can cause a serious adverse reaction (transfusion reaction). Blood is introduced slowly by gravity flow directly into the veins (intravenous infusion) so that medical personnel can observe the patient for signs of adverse reactions. People who have received many transfusions may develop an immune response to some factors in foreign blood cells (see below). This immune reaction must be evaluated before the patient is given new blood.
Adverse reactions to mismatched blood (transfusion reaction) is a major risk of blood transfusion. Transfusion reaction occurs when antibodies in the recipient's blood react to foreign blood cells introduced by the transfusion. The antibodies bind to the foreign cells and destroy them. This destruction is called a hemolytic reaction. In addition, a transfusion reaction may also cause a hypersensitivity of the immune system that may in turn result in tissue damage within the patient's body. The patient may also have an allergic reaction to mismatched blood.
The first symptoms of transfusion reaction are a feeling of general discomfort and anxiety. Breathing difficulties, flushing, and a sense of pressure in the chest or back pain may also be present. Evidence of a hemolytic reaction can be seen in the urine, which will be colored from the hemoglobin leaking from the destroyed red blood cells. Severe hemolytic reactions are occasionally fatal. Reactions to mismatches of minor factors are milder. These symptoms include itchiness, dizziness, fever, headache, rash, and swelling. Sometimes the patient will experience breathing difficulties and muscle spasms. Most adverse reactions from mismatched blood are not life-threatening.
Infectious diseases can also be transmitted through donated blood and constitute another major risk of blood transfusion. The infectious diseases most often acquired from blood transfusion in the United States are hepatitis and HIV.
Patients who are given too much blood can develop high blood pressure, a concern for people who have heart disease. Very rarely, an air embolism is created when air is introduced into a patient's veins through the tubing used for intravenous infusion. The danger of embolism is greatest when infusion is begun or ended. Care must be taken to ensure that all air is bled out of the tubing before infusion begins, and that the infusion is stopped before air can enter the patient's blood system.
Most individuals will feel only a slight sting from the needle used during the blood donation process, and will not experience any side effects after the procedure is over. Plasma is regenerated by the body within 24 hours, and red blood cells within a few weeks. Patients who receive a blood transfusion will usually experience mild or no side effects.
The risk of acquiring an infectious disease from a blood transfusion is very low. The risk of HIV transmission is one in 450,000 to 660,000 units of blood; hepatitis B virus (HBV), one in 137,000 units; and hepatitis C virus (HCV), one in 1,000,000 units. Bacterial contamination (a cause of infection) is identified in one in 4,200 transfusions. Approximately one in 25,000 individuals who receive a blood transfusion will develop a hemolytic reaction; the risk of a fatal hemolytic reaction is one in 160,000.
There are several alternatives to blood transfusion as of 2003. These include:
Berkow, Robert, ed. Merck Manual of Medical Information. Whitehouse Station, NJ: Merck Research Laboratories, 1997.
Lefevre, Patrice, and Pascale Poullin. "Current Information on Risks of Allogenic Blood Transfusion." In Transfusion Medicine and Alternatives to Blood Transfusion. Chatillon, France: Network for Advancement of Transfusion Alternatives, 2000.
American Association of Blood Banks (AABB). 8101 Glenbrook Road, Bethesda, MD 20814-2749. (301) 907-6977. http://www.aabb.org .
American Red Cross (ARC) National Headquarters. 431 18th Street, NW. Washington, DC 20006. (202) 303-4498. http://www.redcross.org .
America's Blood Centers. 725 15th St., NW, Suite 700, Washington, DC 20005. (202) 393-5725. http://www.americasblood.org .
National Blood Data Resource Center (NBDRC). 8101 Glenbrook Road, Bethesda, MD 20814-2749. (301) 215-6506. http://www.nbdrc.org .
American Association of Blood Banks. Facts about Blood and Blood Banking . Bethesda, MD: American Association of Blood Banks, June 2002 [cited February 27, 2003]. http://www.aabb.org/All_About_Blood/FAQs/aabb_faqs.htm .
"Hemopure (HBOC-201) Shows Promise as Alternative to Red Blood Cell Transfusion in Elective Orthopedic Surgery." Doctor's Guide , January 28, 2002 [cited February 27, 2003]. http://www.pslgroup.com/dg/21371a.htm .
National Blood Data Resource Center. National Blood Data Resource Center: FAQs. Bethesda, MD: National Blood Data Resource Center, 2002 [cited February 27, 2003]. http://www.nbdrc.org/faqs.htm .
John T. Lohr, PhD Stephanie Dionne Sherk
Blood may be donated at hospital donor centers, Red Cross chapter houses, or other locations where special blood drives have been organized (churches, places of business, schools, colleges, etc.). The procedure of blood donation is generally performed by a nurse or phlebotomist (a person who has been trained to draw blood). Blood transfusions are generally administered in a hospital or emergency center with a blood bank.