What is a blood transfusion?

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The introduction of whole blood or blood components (such as platelets, red blood cells, or fresh-frozen plasma) directly into the bloodstream.
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Indications and Procedures

Blood transfusion is the introduction of whole blood or blood components directly into the bloodstream. Human blood has been transfused with success since the early nineteenth century. Modern transfusion therapy, however, is largely the result of scientific advances made during the twentieth century and is, therefore, a young discipline. Blood transfusion plays a critical role in modern medical practice by enabling physicians to provide care, both surgical and nonsurgical, which is not feasible in its absence. Until relatively recent times, transfusion options were limited to two items: whole blood and plasma. The introduction of blood component therapy in the 1960s had a major impact on transfusion practice.

Physicians are now able to choose from a large variety of specific blood products. Some products are the result of manufacturing processes that concentrate a portion of blood (blood derivatives), such as factor VIII concentrates for the treatment of hemophilia A. Other products, such as red blood cells or platelet concentrates (blood components), are separated, produced, and distributed by blood collection facilities for transfusion purposes. The cardinal principle of modern transfusion therapy is to administer the specific blood products that patients require. Portions of blood not required by the patient should not be transfused. Therefore, indications for the use of whole blood are very limited and its use is considered, in general, to be wasteful. The two major categories of transfusion are autologous and allogeneic. Autologous transfusion is the infusion of an individual with his or her own blood. Allogeneic transfusion is the infusion of blood collected from a person or people other than the transfusion recipient.

Autologous transfusion. There are four distinct types of autologous blood transfusion services available: preoperative donation, intraoperative hemodilution, intraoperative blood collection and reinfusion, and postoperative collection and reinfusion.

Patients scheduled for surgical procedures in which blood transfusion is likely are candidates to donate and store their own blood in advance for use at the time of surgery . This is preoperative donation. It may be possible to collect and store multiple units of blood with this technique. Close communication between patient and physician is critical in preoperative donation because the number of autologous units required must be determined and a donation schedule must be established. Usually, the last donation occurs no later than seventy-two hours before the scheduled operation. For surgical procedures in which the likelihood of transfusion is remote, preoperative donation has not proven to be cost-effective.

Intraoperative hemodilution is the removal of one or more units of blood from a patient at the beginning of an operation for reinfusion during or at the end of the procedure. The volume of blood removed is replaced by the infusion of solutions that contain no blood cells and no risk of infection, such as Ringer’s lactate or albumin. Intraoperative hemodilution is considered beneficial for a number of reasons. First, this technique lowers blood viscosity (that is, it thins the blood), which may improve blood flow to vital organs. Second, the amount of actual blood loss during the operation is decreased because the patient’s blood is diluted at the start of the surgery. Third, a supply of fresh, normal autologous blood for transfusion is available during and at the end of the surgery.

Intraoperative blood collection and reinfusion refers to the collection and return of blood recovered from the operative field or from machines used for the performance of an operation, such as a return of blood from the cardiopulmonary bypass machine used in cardiovascular surgery. Intraoperative autologous transfusion has proven to be an effective form of blood conservation in a number of surgical procedures, including cardiac, vascular, orthopedic, urologic, trauma, gynecologic, and transplantation surgeries.

Postoperative blood collection and reinfusion refers to the collection and return of blood recovered from surgical drains following an operation. This technique has been used predominantly following cardiac or orthopedic surgery.

The different types of autologous transfusion should not be considered independently of one another. A coordinated approach using multiple techniques offers the greatest opportunity to maximize the value of autologous transfusion and minimize the chance that allogeneic transfusion will be required.

Allogeneic transfusion. This type of therapy begins with blood collection from informed, healthy donors. The allogeneic blood supply in the United States has never been as safe as it is at present. Blood donors are selected according to criteria designed to maximize donor safety and minimize recipient risks. Donor selection criteria are based on a high standard of medical practice and must comply with federal, state, and local regulations concerning blood collection. Facilities that collect and/or process blood and blood components for transfusion must comply with the United States Public Health Service’s “Current Good Manufacturing Practice for Blood and Blood Components.” These manufacturing practices are defined by the Code of Federal Regulations and are administered by the Food and Drug Administration (FDA). State and local laws often govern blood donor age requirements and the filing of reports, such as to state and county health departments, pertaining to donors whose laboratory tests reveal the presence of infectious diseases. There are similar procedures in countries other than the United States as well.

Blood donor selection starts with education regarding donor qualifications. Prior to every donation, potential blood donors are given information about Human immunodeficiency virus (HIV) and Acquired immunodeficiency syndrome (AIDS) . Information is provided on the potential of HIV transmission to individuals receiving blood and on risk behaviors associated with HIV infection. Potential donors are informed of the absolute necessity of refraining from donation if they are at risk for HIV infection. Honest donor self-exclusion is a critical step in maintaining a safe blood supply.

The next phase of the donation process is the health history interview. Confidential interviews, often consisting of both a self-administered questionnaire and direct questioning, are conducted prior to every blood donation. Prospective donors are also tested for hemoglobin level (to check for the presence of anemia), temperature, pulse, and blood pressure. Some individuals are excluded because it is determined that blood donation poses an unacceptable health risk for the donor. Some exclusions, such as when a donor has a history of infectious disease or risk factors for HIV infection, are designed to protect blood recipients. Prospective donors are allowed to terminate the blood donation process at any time. Prior to the start of the actual blood donation, eligible donors are given the opportunity to ask additional questions and provide additional information. They are then asked to sign an informed consent statement. Some individuals may feel obligated to donate blood despite the realization that they do not qualify as safe donors. In this situation, donors are provided another opportunity to disqualify themselves through confidential unit exclusion (CUE). In CUE, blood donors choose “Transfuse” or “Do Not Transfuse” by marking a form or selecting a bar code label following the blood donation.

Laboratory testing of donor blood is required before whole blood or blood components can be made available for routine transfusion. A blood sample from every donation must pass an FDA-licensed test and be found to be negative for hepatitis B surface antigen (HBsAg) and for antibodies to HIV viruses types 1 and 2 (anti-HIV 1/2), hepatitis B core antigen (anti-HBc), hepatitis C virus (anti-HCV), human T-cell lymphotropic viruses types I and II (anti-HTLV-I/II), and West Nile virus. Other tests routinely performed with every donation include a test for syphilis and a test for liver function called the alanine aminotransferase (ALT) level; these tests must be negative and normal, respectively.

Units of blood collected for “Autologous Use Only” at blood centers are ordinarily tested for syphilis, anti-HIV 1/2, HBsAg, anti-HCV, and anti-HBc. Blood units remain acceptable for autologous transfusion despite positive results in one or more tests. Some health care facilities collect Autologous Use Only blood components for transfusion within the institution. Such blood components drawn, stored, and infused at one facility may have not been tested for all the above-mentioned infectious diseases. If autologous blood donors have been screened and tested in a manner identical to allogeneic blood donors, unused autologous blood may be used for allogeneic blood transfusions. Most transfusion services, however, opt to destroy unused autologous blood.

The transfusion process begins with a physician’s assessment of patient need and a formal order, clearly identifiable in the patient record, specifying the blood product to be transfused, the quantity, and any special administration requirements. This order is then transcribed to a special transfusion request form; computer-transmitted requests are acceptable as long as the required information is present. Forms requesting blood or blood components and forms accompanying blood samples from the patient must contain sufficient information for positive identification of the recipient. The first and last name and unique identification number of the patient are required. With the exception of extreme emergencies, such as patients who will bleed to death if there is any delay in transfusion of blood or blood components, the ABO (A, B, AB, or O) and Rh (positive or negative) types of the intended recipient must be determined before blood or blood components are issued for transfusion.

If the patient is to receive whole blood, red blood cells, granulocytes, or platelet components containing more than five milliliters of red cells (red cell–containing components), the recipient’s serum (plasma lacking coagulation factors) must also be tested for the presence of clinically significant unexpected antibodies and for compatibility with the donor red blood cells. The only expected antibodies in a patient’s serum are those directed at the A and/or B groups. Individuals who are in blood group O have antibodies directed toward the A and B groups, those who are in group A have anti-B antibodies, and group B individuals have anti-A antibodies. People who are in group AB do not have antibodies directed toward the A or B groups. There is no anti-O antibody. If the serum of a prospective transfusion recipient contains a clinically significant unexpected red cell antibody, red cell-containing components chosen for transfusion must lack the corresponding antigen (the determinant to which the antibody is directed).

With the exception of emergencies, the recipient’s serum is usually tested with red blood cells from the donor prior to the release of red cell–containing components for transfusion. This procedure is known as the major crossmatch, and if recipient serum does not react with donor red cells, the red cell–containing unit is termed crossmatch compatible. It is now acceptable to use properly functioning computer systems to select compatible red cell units for transfusion in the place of a major crossmatch for recipients who do not have clinically significant unexpected antibodies. Blood components that do not contain five milliliters or more of red blood cells, such as fresh-frozen plasma, cryoprecipitate, and most platelet components, do not have to be crossmatched.

Patients should receive blood and blood components of their own ABO group whenever possible. For red cell–containing components, with the exception of whole blood, alternative choices exist when ABO identical components are not available. For red cell–containing components, the donor red cells must be compatible with the recipient’s plasma. For example, group A recipients may receive group O red blood cells. When transfusing components that contain plasma (whole blood, fresh-frozen plasma, cryoprecipitate, or platelets), it is best to transfuse blood products that are compatible with the recipient’s red blood cells. For example, group A recipients may receive group AB fresh-frozen plasma since the plasma from group AB donors does not contain anti-A. Whole blood transfusion should be ABO identical because donor red cells and plasma must be compatible with the recipient.

For whole blood, red blood cells, platelets, and granulocytes, Rh-identical products should be provided whenever possible. Rh-negative units are acceptable for transfusion into Rh-positive individuals, but Rh-negative units should be reserved for Rh-negative recipients because of the limited supply of Rh-negative blood. The transfusion of Rh-positive blood into Rh-negative recipients will likely result in the formation of antibodies to the Rh antigen and therefore should be avoided in all but emergency situations. Rh type is not a consideration when transfusing fresh-frozen plasma or cryoprecipitate.

When there is a desperate requirement for blood, there may be a need to transfuse uncrossmatched red blood cells. If the recipient ABO group and Rh type are unknown, group O red cells should be transfused, and it is preferable that they be Rh negative. If there has been time to determine the recipient’s ABO and Rh types with a current blood sample, then appropriate ABO and Rh type blood can be issued uncrossmatched (that is, uncrossmatched A-positive red cells can be provided to a recipient determined to be A positive). Previous records must not be used to determine which blood group to issue, nor may the recipient’s blood type be taken from other records such as credit cards, dog tags, or a driver’s license.

Whole blood. A unit of whole blood contains approximately 450 milliliters of blood and 63 milliliters of anticoagulant/preservative solution. All the elements that make up human blood are in whole blood. Whole blood stored for more than twenty-four hours, however, contains few functional platelets or white blood cells. In addition, the levels of two proteins in whole blood necessary for normal blood clotting, known as coagulation factors V and VIII, decrease with storage. Stored whole blood, therefore, cannot be considered a source of functional platelets, functional white cells, or therapeutic levels of coagulation factors V and VIII. Whole blood provides oxygen-carrying capacity and blood volume expansion. Oxygen-carrying capacity is accomplished through the red blood cells present in whole blood. Red blood cells carry oxygen, which they deliver to vital organs and tissues. The approximately 500-milliliter volume of a unit of whole blood may make a significant addition to the total blood volume of a patient. The maintenance of a normal blood volume is vital to maintaining a proper level of pressure within the vascular system to get blood to and from vital organs and tissues. Patients lacking in blood volume may benefit from the volume provided by whole blood. Whole blood transfusions may be used, therefore, when there is a need for blood volume support combined with oxygen-carrying capacity, such as in patients experiencing severe acute hemorrhage.

For patients requiring oxygen-carrying capacity only, such as patients who have a normal blood volume but are anemic, red blood cell transfusion is recommended. When blood volume support is the sole need, such as in the early stages of acute blood loss when oxygen-carrying capacity has not yet become compromised but the blood volume is diminished, blood volume expanders that pose no risk of infectious disease—for example, normal saline (a salt and water solution)—are favored. Whole blood and other red cell components should not be used in patients with anemias that can be treated safely with specific medications such as iron, vitamin B12, recombinant erythropoietin, or folic acid. Coagulation factor deficiencies, such as hemophilia, are more effectively treated with other blood components or derivatives. The storage period for whole blood varies from twenty-one to thirty-five days, based on the type of anticoagulant/preservative solution. As a result of time constraints posed by prerelease testing, whole blood that is less than twenty-four hours old is not routinely available. Whole blood stored less than seven days is often considered a desirable blood product for exchange transfusions in neonates (newborn children).

Red blood cell components. These components are produced when centrifugal or gravitational separation of red cells from plasma in whole blood is followed by the removal of 200 to 250 milliliters of plasma. The storage period of red cells collected and stored in an anticoagulant/preservative solution known as CPDA-1 is thirty-five days. Many red cell components contain a supplemental additive solution in addition to the anticoagulant/preservative. Additive systems extend the storage period for red blood cells to forty-two days. Red cell transfusions increase oxygen-carrying capacity by increasing the circulating red blood cell mass. Increasing oxygen delivery to the body’s organs and tissues with red cell transfusions may correct or prevent the manifestations of anemia. Red cell transfusions should be administered to patients with symptomatic anemia when other treatments are unavailable or ineffective and to those patients for whom rapid replacement of red cell mass is of critical importance. A unit of red blood cells contains essentially the same number of red cells as a whole blood unit. The volume of a red cell unit, however, is approximately 50 to 66 percent of whole blood. Thus, the use of red cells allows for the delivery of more red cells per milliliter transfused than whole blood, and smaller volume transfusions are required to achieve desired increases in oxygen-carrying capacity. When red blood cell components are used for exchange transfusion, it is common to use units that are less than seven days old. Stored red blood cells do not contain functional platelets or white blood cells.

In adults, a hemoglobin value of seven grams per deciliter or less is commonly used as a guideline for red cell transfusion. (An example of a normal range for hemoglobin is 13.5 to 16.5 grams per deciliter in adult men and 12.0 to 15.0 grams per deciliter in adult women.) This is a useful guideline; however, the decision to transfuse red cells should be based on patient clinical status. Laboratory data should be utilized as part of overall patient assessment and not as a sole indicator for transfusion therapy. Signs and symptoms reflecting a possible need for red cell transfusion include fainting, shortness of breath, a drop in blood pressure when sitting up or standing up, rapid heart rate, chest pain, and transient neurologic deficits. In rapid acute blood loss, the hemoglobin value may not reflect circulating red cell mass. Red cell transfusion decisions in this setting are based on assessments of blood loss, cardiorespiratory status, and oxygen delivery to tissues. Certain diseases compromise oxygen delivery to tissues or the adequate oxygenation of red blood cells, such as heart disease, lung disease, and disease of the blood vessels supplying the brain. Such patients may need to be transfused at higher hemoglobin levels than other patients in order to maintain adequate organ and tissue oxygenation. In summation, the decision to transfuse red cells should be based on patient symptoms, laboratory data, underlying diseases, and the urgency of need for oxygen-carrying capacity.

In neonates, red cell transfusions are usually small in volume (five to ten milliliters per kilogram) and administered frequently. The most common indication for red cell transfusion in neonates is to replace blood drawn for laboratory studies. Blood losses caused by laboratory sampling are proportionately large in neonates because of their small blood volumes. Usually, red cells are transfused following the removal of 5 to 10 percent of the estimated blood volume from sick neonates requiring frequent monitoring. Neonates with severe respiratory disease, particularly those requiring oxygen and/or respiratory support, are usually transfused to maintain a hematocrit level (a laboratory test used as a marker for anemia) above 40 percent. An example of a normal range for hematocrit values in children is 40 to 50 percent. Similar transfusion guidelines have been established for neonates with congenital heart disease. In neonates without severe respiratory or heart disease, it has been recommended that red cell transfusions be given to maintain hematocrit levels above 30 percent for infants with shortness of breath, rapid breathing, episodes of no breathing, rapid heart rate, and abnormal heart rhythms. Some physicians advocate red cell transfusions to maintain hematocrit levels above 30 percent for infants experiencing poor weight gain.

Red cell components may be modified by centrifugation, filtration, washing, sedimentation, or freezing/thawing to remove white blood cells. White cell removal procedures must result in a component that contains fewer than 5x108 residual white blood cells while maintaining at least 80 percent of the original red cells. Many white cell filters achieve much higher levels of white cell removal. White cell–depleted blood components are used to prevent febrile transfusion reactions (fever), to prevent or delay alloimmunization to white blood cell antigens, to prevent poor responses to platelet transfusions as a result of alloimmunization, and to prevent the transmission of white blood cell–associated viruses, such as cytomegalovirus, by cellular blood components.

Automated techniques are available for the washing of red cell units with sterile saline. This is less effective than filtration for white blood cell removal. The washing of red cells, however, does remove as much as 99 percent of the plasma from the red cell unit. Washed red cells may be indicated for patients requiring minimal plasma exposure. Examples include patients with a disease known as paroxysmal nocturnal hemoglobinuria, patients with IgA antibodies, and patients who have experienced recurrent or severe allergic transfusion reactions. Signs and symptoms of allergic reactions include hives, wheezing, low blood pressure, swelling of the throat, and fluid in the lungs.

Frozen red cells are prepared through the addition of glycerol, a cryoprotective (cold-protecting) agent, to red cells that are usually less than six days old, followed by freezing. The storage period for frozen red cells is up to ten years from the date that the unit was collected. When needed for transfusion, frozen red cells are thawed and washed with a series of saline-glucose solutions to remove glycerol. The unit is resuspended in sterile saline or a saline-glucose mixture. After thawing, washing, and resuspension, the storage period is twenty-four hours at one to six degrees Celsius. Frozen/thawed red cells are virtually devoid of plasma, anticoagulant, and platelets. The degree of white cell removal with this procedure is comparable to current filtration methods. Freezing is useful for the storage of rare red cell units and for the long-term preservation of autologous red cells. Because frozen/thawed red cells contain minimal amounts of plasma and white blood cells, they may be used when leukocyte-depleted and/or plasma-depleted red cell units are indicated.

Platelets. Platelet concentrates are prepared from whole blood by centrifugation. Most platelet concentrates contain at least 5.5x1010 platelets. The usual storage period for platelet concentrates is five days at twenty to twenty-four degrees Celsius. Platelets are often administered as a pool of concentrates.

Apheresis platelets are the second type of platelet component available. They are collected from a donor through the use of a blood cell separator in a procedure known as plateletpheresis. Most apheresis platelets contain at least 3x1011 platelets. An apheresis platelet (collected from one donor) is the equivalent of six to eight units of platelet concentrates. Apheresis platelets are sometimes beneficial in patients who are not responding satisfactorily to platelet concentrates because of antiplatelet antibodies (alloimmunization). Antiplatelet antibodies often arise in response to human leukocyte antigens (HLAs) present on donor platelets; these antigens aid the immune system in recognizing “self” or “nonself” material. Donors possessing HLAs that are identical or similar to those of the recipient may be selected to provide platelets for transfusion. Such components are known as HLA-matched platelets. Apheresis platelets can be used to decrease the number of blood donor exposures for a recipient and to reduce or delay the development of alloimmunization.

A low number of platelets (less than fifty thousand per cubic millimeter) is known as thrombocytopenia ; the normal range for platelets is 150,000 to 400,000 per cubic millimeter of blood. Thrombocytopenia may result from disease processes, such as leukemia or aplastic anemia, or from the medical treatment of diseases, such as the use of chemotherapy for the treatment of cancer. Thrombocytopenia can lead to bleeding problems. Patients with functionally abnormal platelets may experience bleeding and have normal platelet counts. Platelet transfusions may be indicated to treat significant active bleeding or to protect against bleeding prior to invasive procedures, such as major surgery, in patients with platelet dysfunction or thrombocytopenia. Prophylactic platelet transfusions are commonly administered to prevent bleeding in patients with thrombocytopenia caused by decreased platelet production, as with cancer therapy. A commonly accepted threshold for prophylactic platelet transfusion in such patients is a platelet count of less than twenty thousand per cubic millimeter. Platelet transfusions are usually not effective in the setting of rapid platelet destruction, such as in a condition known as idiopathic (or autoimmune) thrombocytopenic purpura (ITP). Platelets are also not recommended for routine use in a condition known as thrombotic thrombocytopenic purpura (TTP). In the event of life-threatening hemorrhage in ITP or TTP, however, platelet transfusions may be necessary.

Prophylactic platelet transfusions are recommended for all neonates with a platelet count less than twenty thousand per cubic millimeter. In the presence of active bleeding or prior to invasive procedures, platelet transfusions are recommended to keep the platelet count above fifty thousand per cubic millimeter. In stable premature neonates, prophylactic platelet transfusions are recommended to maintain a platelet count above fifty thousand per cubic millimeter. In sick premature neonates, platelet transfusions are given to maintain a platelet count above 100,000 per cubic millimeter.

Fresh-frozen plasma. The fluid portion of whole blood is called fresh-frozen plasma (FFP). It can be separated and frozen at -18 degrees Celsius or colder within eight hours of whole blood collection. FFP may be stored for up to one year at -18 degrees Celsius or colder. It contains all plasma proteins present in normal blood.

FFP may be used to treat isolated deficiencies of coagulation proteins (factors II, V, VII, IX, X, and XI) when more specific components are not available or appropriate. Patients on oral anticoagulant therapy, such as warfarin, may require FFP to reverse anticoagulant effect rapidly prior to emergency invasive procedures or because of active bleeding. Depletion of multiple coagulation factors may occur in patients who have developed a deficiency of vitamin K, in those patients receiving massive blood replacement, or with a condition known as Disseminated intravascular coagulation (DIC) . The use of FFP may be necessary to treat such problems. FFP may be required for patients with liver disease who are actively bleeding or who face invasive procedures. FFP contains antithrombin III (AT-III), a naturally occurring anticoagulant, and it may be used in patients requiring AT-III. Plasma components, either through simple transfusion or as part of plasma exchange procedures, have become a vital aspect of therapy for TTP.

Indications for FFP in neonates include liver failure, inherited coagulation factor deficiencies, bleeding caused by vitamin K deficiency, the treatment of DIC, protein C deficiency (another naturally occurring anticoagulant), and AT-III replacement therapy.

FFP is not recommended for coagulation abnormalities that can be treated more effectively or safely with specific therapy such as vitamin K (in less serious situations, vitamin K deficiency is treated with vitamin K replacement instead of FFP), cryoprecipitate, or specific coagulation factor concentrates. FFP should not be used as a volume expander or as a nutritional source.

Cryoprecipitate. A concentrated source of certain plasma proteins, cryoprecipitate is a white precipitate that forms when FFP is thawed at between one and six degrees Celsius. The cryoprecipitate is removed and refrozen at -18 degrees Celsius or colder. A single bag of cryoprecipitate has a volume of ten to fifteen milliliters. Cryoprecipitate has a storage period of one year when stored at -18 degrees Celsius or colder. Several proteins necessary for normal blood clotting are present in cryoprecipitate, including factor VIIIc, von Willebrand factor (vWF), fibrinogen, and factor XIII.

Cryoprecipitate is used in the treatment of hemophilia A (a deficiency or abnormality of factor VIIIc), von Willebrand disease (a deficiency or abnormality of vWF), inherited or acquired fibrinogen deficiency or dysfunction, and factor XIII deficiency. Cryoprecipitate has been beneficial in some kidney disease patients with abnormal bleeding. It is used to prepare fibrin glue, a material with adhesive and hemostatic properties that has been shown to be of value as a sealant in many operative procedures.

Granulocytes. Units of white blood cells (granulocytes) may be obtained by apheresis or by removal from units of fresh whole blood. Granulocytes collected by apheresis have a volume of two hundred to three hundred milliliters and should contain more than 1.0x1010 granulocytes. To maximize therapeutic effect, granulocytes should be transfused as soon as possible following preparation. If storage is necessary, granulocytes may be stored for twenty-four hours at twenty to twenty-four degrees Celsius.

Granulocyte transfusions have been used to aid in the treatment of serious infections in patients with dysfunctional or very low numbers of white blood cells who are not responding to conventional therapies. Neonates with blood infections (sepsis) may receive granulocyte transfusion as a supplement to antibiotic therapy.

Uses and Complications

The use of autologous transfusion has increased markedly since the mid-1980s. This increase is largely the result of concerns of patients and physicians about the transmission of certain diseases, such as AIDS and hepatitis. In addition to minimizing the risk of transmitting such diseases, autologous transfusion provides numerous other advantages. Alloimmunization, the formation of antibodies to substances (alloantigens) present in allogeneic blood, will not occur when autologous blood is used. Some patients requiring blood transfusion are already alloimmunized from previous allogeneic transfusion or from pregnancy. The provision of compatible allogeneic blood to such patients can sometimes be difficult. Therefore, the availability of autologous blood in these situations, when possible, is advantageous.

A number of transfusion reactions may result from exposure to allogeneic blood—allergic reactions, fever, hemolytic reactions, graft-versus-host disease (GVHD)—which are prevented with autologous blood. Allogeneic blood appears to suppress the immune systems of transfusion recipients. Although there is still much to be learned about this phenomenon, the effect may adversely influence recurrence rates and mortality following some forms of cancer surgery and may lead to increased susceptibility to viral and bacterial infections. Autologous blood usage avoids these potential immunosuppressive effects. The use of autologous blood also leads to the conservation of vital blood resources. In the absence of the availability of autologous blood, transfusion needs must be met through the use of a volunteer allogeneic blood supply. For practical purposes, transfused autologous blood can be thought of as conserving a like amount of allogeneic blood. The availability of autologous blood may also lessen patient anxiety regarding the need for transfusion.

The overall risk of HIV infection from allogeneic blood transfusion is estimated at one in 225,000 per unit of blood (whole blood and blood components). The transfusion-transmitted infection rates for hepatitis B virus, HTLV-I/II, and HCV are estimated to be one in 200,000, one in 60,000, and one in 3,300 per unit, respectively. Although fear of HIV infection is a primary concern of transfusion recipients, transfusion-transmitted HCV infection is the principal infectious disease risk. The incidence of other transfusion-transmitted infections is very low in countries such as the United States. The current estimate of risk is less than one in one million per unit for transfusion-transmitted yersiniosis (Yersinia enterocolitica infection), malaria, babesiosis, and Chagas disease (trypanosomiasis).

Transfusion-associated GVHD is a rare but severe complication of transfusion therapy. While patients with underdeveloped or impaired immune systems are at the greatest risk for developing this disease, it can occur in patients with normal immune systems. The transfusion of blood and blood components donated by blood relatives may put a recipient at risk for transfusion-associated GVHD. Gamma irradiation of whole blood and cellular blood components is the only acceptable method to reduce the risk. Fresh-frozen plasma and cryoprecipitate have not been implicated in this disease.

It is an absolute necessity that proper identification of recipients be obtained prior to any transfusion procedure. Transfusing facilities must have strict policies to guarantee that the appropriate types of blood or blood components are transfused to the correct patients. Blood and blood components are visually inspected prior to their release for transfusion. If their fitness is questioned upon inspection, they will not be released. Visual abnormalities include hemolysis (evidence of red cell breakage), follicular material, cloudy appearance, or a deviation from the usual color of the blood or blood component. Blood and blood components are prepared by techniques designed to safeguard sterility through their expiration date. Once the seal of a blood component has been broken for any reason, the expiration time is four hours if maintained at room temperature (twenty to twenty-four degrees Celsius) or twenty-four hours if refrigerated (one to six degrees Celsius). All transfusions must be administered through a filter. Transfusion recipients should be observed carefully during the first fifteen minutes of a transfusion. If a life-threatening transfusion reaction occurs, such as from the mistaken transfusion of incompatible red blood cells, it usually develops following the infusion of only a small volume of the blood or blood component. Blood transfusion must be completed prior to the expiration time of the component or within four hours, whichever is sooner. All adverse reactions to transfusion, including possible bacterial contamination or suspected disease transmission, must be reported to the transfusion service.

Perspective and Prospects

The first well-documented transfusion of human blood to a patient was administered by James Blundell on September 26, 1818. For most of the first hundred years of human blood transfusion, blood was transfused from donor to recipient by means of a direct surgical communication between the donor and recipient blood supplies. Numerous transfusion-related fatalities resulted, probably from the infusion of incompatible blood. A landmark event in the history of transfusion medicine occurred in 1901 when Karl Landsteiner published his observations that the sera of some individuals causes the red cells of others to agglutinate (clump). This led to the discovery of the ABO blood group system and set the stage for safe transfusion therapy. Reuben Ottenberg and David J. Kaliski subsequently published their key observations on the importance of pretransfusion compatibility testing in 1913.

Despite these advances, blood transfusion remained a cumbersome technique until the value of blood anticoagulants was noted by multiple investigators in 1914 and 1915. For the first time, blood donation could be separated, in time and place, from blood transfusion. Blood could be drawn and set aside for use at a later time. This led to the development of blood banks for the storage and distribution of blood. The first hospital blood bank in the United States was established at Cook County Hospital in Chicago in the mid-1930s. Blood was collected in glass bottles that were washed, sterilized, and reused following transfusion. The introduction of plastic containers for blood in 1952 led to the development of disposable plastic systems for the collection, separation, and preservation of blood products. The advent of such plastic systems allowed whole blood to be separated easily into multiple blood components, thus setting the stage for modern blood component therapy.

Transfusion medicine has become a vital aspect of modern medical practice. Patients with cancer may be treated more aggressively because of the support provided by blood products. Organ and tissue transplantation (such as liver, kidney, and bone marrow transplants) and other complex surgical procedures have become possible because of blood and blood component therapy.

The use of blood and components is constantly evolving. Continual efforts are being made to maximize the safety and availability of the blood supply. Indications for blood and blood component transfusions continue to be analyzed and clarified. Alternatives to allogeneic blood transfusion, such as autologous transfusion, the use of blood growth factors (such as recombinant erythropoietin), and manufactured blood substitutes (such as oxygen-carrying perfluorochemical solutions), continue to be explored and are expected to receive more widespread application.

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