CHAPTER 38 Transfusion medicine for pathologists
Introduction
The discipline of blood transfusion and transfusion medicine at the beginning of the 21st century involves a complex, structured, standardized and regulated production process along with sophisticated hemotherapy. The laboratory techniques used are far different from those of Landsteiner who discovered the ABO blood group system by observing clumps of red cells or hemolysis when the cells from some of his laboratory workers were mixed with the serum from others. Other chapters in this book beautifully describe current extensive knowledge of the structure and function of blood groups1 and immune hemolytic anemias.2 In developed countries, virtually all whole blood is collected from unpaid volunteer donors by regional, community-based or individual, hospital-based blood banks. The whole blood is separated into its components shortly following donation; thus each component is available for use for the most appropriate specific clinical condition. This approach, called blood component therapy, places responsibility on the clinician to identify the specific blood deficit of the patient and to choose a specific blood component. In this chapter, we will describe the approaches used to obtain blood, the medical uses of blood components and the complications of transfusion.
Blood supply systems throughout the world
Whole blood
Approximately 75 million units of whole blood are collected worldwide, but this almost certainly does not meet worldwide needs. The organizations and systems that collect and provide blood vary greatly throughout the world. Most developed countries, with the exception of the United States, have some form of a national blood program.3 The program may be operated by that country’s Red Cross or by its government. The extent to which this program is structured, the mechanisms of funding, and the effectiveness of the national blood program in meeting the total blood needs for that country also vary greatly throughout the world. In many developing countries the blood supply may be inadequate to meet the needs, and the blood that is available has a high likelihood of transmitting infectious disease.4
The US blood system is operated by multiple organizations.5 Approximately 15 million units of whole blood are collected each year primarily in regional or community blood centers.6 Hospitals collect less than 10% of the US blood supply. The American Red Cross is the largest blood collecting organization in the US, accounting for about 45% of the blood supply. Other regional or community blood centers are non-profit organizations governed by local volunteer boards of directors.
It is policy of the International Society for Blood Transfusion and the World Health Organization that blood should be donated voluntarily. The reason for advocating volunteerism in blood donation is not only based on the moral principle of not selling body parts or tissues but also because blood from paid donors has a much higher risk of disease transmission.7 When a financial payment is involved, there is an incentive for the potential donor to be dishonest about his or her medical history. Despite the increased sophistication of laboratory testing of donated blood, some infectious units of blood will not be detected by present tests.8 Thus, if the donor is dishonest about his or her medical history, there is more likelihood that the unit may be infectious.
In developed countries, the collection, processing, testing and preparation of blood components is subject to some form of regulation. Although blood is a biological, and thus different from a pharmaceutical, some form of pharmaceutical-type regulation is applied.5 Thus, there are requirements for donor eligibility, laboratory testing of donated blood, blood preservation and the minimum content of various blood components. Usually these requirements define procedures, records, staff proficiency, specific testing and donor medical requirements that blood banks must follow. In the US, additional standards have been promulgated by the American Association of Blood Banks – a voluntary organization that accredits blood banks as a way of assuring high quality and providing continued education for blood bank professionals.9,10
Blood donor recruitment
In developed countries, most people will require a blood transfusion at some time in their lives. The blood supply comes from a small group of dedicated donors. In the US, blood donors differ from the general population in that they are more likely to be male, aged 30–50, more highly educated, employed and Caucasian.11 Although there have been some studies of the social psychology and motivation of blood donors,12 the process is not well understood and is likely to vary for different ethnic or cultural groups or countries.12 A recent developing concern is that with the increasingly stringent donor requirements resulting from the AIDS epidemic, a larger portion of the population is being excluded as potential donors. In addition, as the population in many developed countries ages, there is a decreasing portion of the population available for blood donation. In the US, only about a third of the population meets all the donor requirements.13
Plasma
The AIDS epidemic has had a major impact on blood banking and transfusion medicine. Although blood bank professionals believe they acted properly, with reasonable speed, and with the public’s interest in mind to balance blood safety and blood availability, in many countries the public was not satisfied with this response. The plasma industry was subjected to even more severe criticism, particularly from the hemophilia community. Because plasma derivatives, including coagulation factor concentrates, are prepared from large pools of plasma containing plasma from many donors, a large proportion of these derivatives was contaminated with HIV and many hemophiliacs were infected. Although the plasma industry moved expeditiously to introduce pathogen inactivation steps into the manufacturing process, there was a widely held belief that these companies should have implemented these steps sooner. In addition, in some countries, criminal actions were taken successfully against leaders of the blood programs for failure to take certain actions that might have helped to mitigate the impact of the AIDS epidemic on transfusion recipients. As a result of the AIDS epidemic, there has been a substantial increase in the eligibility requirements for blood donors and increase in the number and specificity of questions about donor’s medical history and activities that might place them at risk of being infected with transfusion-transmitted diseases. In addition, the number of tests performed on donated blood has increased and there has also been a fundamental shift in the regulatory philosophy. In most developed countries, the expectation developed that blood donor screening, collection, processing and component production would be carried out much like a pharmaceutical manufacturing process.5,10 In addition, the use of blood products also changed dramatically. Physicians became much more conservative in prescribing blood and more extensive use of guidelines and monitoring of transfusions has occurred.
Whole blood
Collection of whole blood
Blood is collected into plastic bags, each of which is sterile and can be used only once. Often combinations of bags are used so that whole blood can be separated into its components in a closed system, thus minimizing the chance of bacterial contamination while making storage of the components for days or weeks possible. The venipuncture site is an area free of skin lesions; it is scrubbed with a soap solution followed by an iodine solution. Because bacterial contamination of blood can be a serious or even fatal complication of transfusion,14,15 it is important to minimize bacterial contamination by selecting a good venipuncture site and decontaminating it properly.
Adverse reactions to blood donation
Donors have a reaction following approximately 4% of blood donations, but serious reactions are rare. Reactions are more likely to occur in younger, first-time single donors who have a higher pre-donation heart rate and lower diastolic blood pressure.16,17 The most common reactions include mild weakness, cool skin, diaphoresis, lightheadedness and/or nausea. More extensive reactions involve dizziness, pallor, hypertension, nausea and vomiting, bradycardia and/or hyperventilation which sometimes lead to twitching or muscle spasms. Bradycardia indicates a vasovagal reaction rather than hypotensive or cardiovascular shock, where tachycardia would be expected. Other complications of blood donation include hematoma at the venipuncture site and injury to the bracheal nerve and resulting pain and/or paresthesia due to needle puncture of the nerve or compression from a hematoma.18–20 Rare but severe donor reactions involve loss of consciousness, convulsions, serious cardiac difficulties and/or involuntary passage of urine or stool.16,21
Autologous blood donation
In the early 1990s, there was great excitement about the potential of autologous blood and it was estimated that in the US autologous blood could account for 20% of all blood used.22 This has not occurred because much of the autologous blood was collected from patients undergoing procedures with little likelihood of needing blood, surgeons became more skilled at minimizing blood loss, and anesthesiologists became more skilled at managing fluid administration and maintaining patients with lower hemoglobin levels. In 2004, only 3% of donation in the US was autologous.6
Preoperative donation. If an elective procedure is scheduled and there is a high likelihood of blood transfusion, the patient can donate blood in advance for his/her own use. Since the donor is actually a patient, they usually do not meet the regulatory requirements for normal blood donation. Thus, the blood is usually not suitable for use by someone else if it is not needed by the original donor/patient. Thus, it is important that autologous blood be collected only for procedures in which there is substantial likelihood that it will be used. Without this type of planning, there is a very high rate of wastage of autologous blood (estimated at 40.4% in the US in 2004).6 This amount of waste also means that the costs of autologous blood are quite high.23
Perioperative hemodilution (acute normovolemic hemodilution).24 Perioperative hemodilution is carried out in the operating room usually after the patient has undergone general anesthesia. One to two units of whole blood are collected and replaced with an electrolyte solution at three times the volume of blood collected. The patient’s hematocrit is maintained at least at 30%. This procedure does not pose unusual risks to patients who are stable and undergoing elective surgery. If it is carried out prior to surgical procedures in which substantial expected blood loss is expected, the 2 units of freshly collected blood are kept in the operating room and can be transfused to the patient during surgery. Theoretical advantages of perioperative hemodilution, in addition to having the blood available, are that blood loss during surgery occurs at a lower hematocrit and thus there is less red cell loss, that surgery is carried out at lower hematocrit which improves blood viscosity and possibly provides better tissue oxygenation, and that the blood that is available for transfusion is fresh. Perioperative hemodilution must be carried out by a committed, knowledgeable anesthesia staff and it appears to have limited but definite value.
Directed donor blood
Directed donors are friends or relatives who wish to give blood for a specific patient. Usually this is done because the patient hopes those donors will be ‘safer’ than regular blood donors. In some parts of the world, however, directed donation is a necessity because the general blood supply is not adequate. In the US, data do not indicate that directed donors have a lower incidence of transmissible disease markers,25 and thus there is no factual rationale for these donations. Directed donors must meet all of the regulatory requirements for routine blood donation. Their blood becomes part of the community’s general blood supply if it is not used for the originally intended patient.
Therapeutic bleeding
Blood may be collected as part of the therapy for diseases such as polycythemia vera or hemochromatosis. This blood is not usually used for transfusion because the donors do not meet the FDA requirements. As the genetic basis for hemochromatosis has become known, efforts have begun to gain approval for the use of blood obtained from patients with hemochromatosis.26,27 Limited experience suggests that a donor program could be effective, but it is not likely that blood from hemochromatosis patients would have a substantial impact on the nation’s blood supply.28
Preparation, storage, and characteristics of blood components
Cryoprecipitate
Cryoprecipitate was developed originally as a source of factor VIII and was the first concentrated form of this coagulation factor available to treat hemophilia. With the development of coagulation factor concentrates that have undergone viral inactivation, the major use of cryoprecipitate currently is as a source of fibrinogen or as fibrin glue.29
Whole blood-derived platelet concentrates – platelet-rich plasma method
Platelets can be produced from units of whole blood or by plateletpheresis. In the US, when platelets are prepared from whole blood, the unit of whole blood is maintained at room temperature and centrifuged, and the platelet-rich plasma is passed into a satellite bag. The platelet-rich plasma is centrifuged again, and the platelet-poor plasma is passed into another satellite bag leaving the platelet concentrate which has a volume of proximately 50 ml. At least 75% of random donor-platelet concentrates contain at least 5.5 × 1010 platelets. Four to six units of random-donor platelets are pooled to provide a therapeutic dose for transfusion. These whole blood-derived platelet concentrates may then be stored for up to 5 days at room temperature (20–24°C). The variables known to be important in platelet preservation are: temperature, method of agitation, volume of suspending plasma and type of storage container. At the end of the storage period, the intravascular recovery and half-life of the stored platelets are approximately 51% and 3.1 days.30
Whole blood-derived platelet concentrates – buffy coat method
In some countries, the whole blood is centrifuged and the buffy coat containing leukocytes and platelets is removed.31 Buffy coats from several units are pooled, the pooled buffy coats are centrifuged, and the platelets are separated from the leukocytes to provide a platelet concentrate. This method provides a therapeutic dose of platelets and no further pooling is necessary. It is thought that this method of preparation provides better platelet function,31 although it has not been adopted in the US.
Collection and production of blood components by apheresis
Blood components can also be prepared by apheresis.32 Whole blood is pumped out of one arm, anticoagulant is added, and the blood is passed through an instrument in which it is centrifuged and separated into red cells, plasma, and a leukocyte/platelet fraction. One of the components is removed and the remainder of the blood is returned via the other arm. This process enables a larger number of cells to be obtained than would be available in one unit of whole blood. Several semi-automated instruments are available for the collection of platelets, granulocytes, peripheral blood stem cells, mononuclear cells, plasma or red cells.32 Some newer instruments allow collection of different combinations of components, such as plasma and platelets.
Platelet concentrates
Plateletpheresis usually takes about 90 minutes during which about 4000–5000 liters of the donor’s blood are processed through the blood cell separator. These platelet concentrates have a volume of about 200 ml and contain about 3.5 × 1011 platelets and less than 0.5 ml of red cells. This provides a therapeutic dose of platelets for transfusion. Plateletpheresis has been used increasingly so that in the US about 80% of platelets are produced by plateletpheresis,6 but plateletpheresis is much less common in many other countries.
Granulocyte concentrates
Because of the small number of circulating granulocytes, it is not practical to prepare granulocyte concentrates from whole blood donations. Instead, leukapheresis is used to process 6.5–8.0 ml of donor blood during about three hours32 and obtain a granulocyte concentrate. Hydroxyethyl starch is added to the blood cell separator flow system to sediment the red cells and improve the separation of granulocytes from other blood components. To increase the donor’s peripheral blood granulocyte count, and thus increase the yield of granulocytes, dexamethasone and recently, granulocyte colony-stimulating factor (G-CSF) has been administered to granulocyte donors.33
Peripheral blood stem cells
Hematopoietic stem cells present in the peripheral blood that are capable of providing complete hematopoietic reconstitution in humans stimulated the development of methods to collect peripheral blood stem cells by cytapheresis.33,34 The number of peripheral blood stem cells (PBSCs) circulating under usual conditions is low but following chemotherapy there is a rebound and a large number of PBSCs can be obtained by apheresis. G-CSF is also given to patients or normal donors to increase the number of circulating PBSCs and provide an adequate dose of cells for successful reconstitution of hematopoiesis.35,36 Usually approximately 1 × 1010 mononuclear cells and 2–6 × 107 CD34+ cells are obtained after processing up to 15 l of the donor’s blood during 4–5 hours. The concentrate has a volume of about 200 ml.
Selection of apheresis donors
The criteria and requirements for donors of whole blood apply to the selection of donors for apheresis;37 however, there are some additional requirements. These may vary in different countries, but they generally define the volume of blood that can be extracorporeal during apheresis, the volume of red cells or plasma that can be removed in a given time, the frequency of donation, and any laboratory tests in addition to those performed for whole blood donation. The laboratory testing of donors for transmissible diseases is the same as that for whole blood donation. Thus, the likelihood of disease transmission from apheresis components is the same as that from components prepared from whole blood.
Reactions in apheresis donors
In general, the types of adverse reactions that occur following cytapheresis are similar to those following whole blood donation. However, some side-effects or reactions unique to cytapheresis occur.32 These include paresthesias due to the infusion of the citrate used to anticoagulate the donor’s blood while it is in the cell separator; myalgia, arthralgia, headache, or flu-like symptoms due to G-CSF in granulocyte donors;32,37 or headache and/or hypertension from blood volume expansion due to the sedimenting agent hydroxyethyl starch used in the cell separator to improve the granulocyte yield.
Laboratory testing of donated blood
Blood is tested for the ABO and Rh type, and red cell antibody screening (detection) is performed. Tests for cytomegalovirus, HLA antibodies or rare red cell antigens may be done depending on the needs of the blood bank and the patients it serves. Because of the large amount of laboratory and donor data, today’s blood center uses pharmaceutical-type manufacturing processes and complex computer and quality control systems in order to ensure accuracy and safety.5,9,10
Compatibility testing (crossmatching)
Compatibility testing includes all the steps and procedures involved in providing blood cells that will have an acceptable in vivo survival. The crossmatch is only one part of compatibility testing. Other steps in compatibility testing include ABO Rh typing of donor red cells, acquiring a proper sample from the patient, ABO Rh typing of the patient, testing the patient’s serum for red cell antibodies, selecting the proper blood component, carrying out the crossmatch, labeling the component with the identity of the recipient and release of the unit from the blood bank. The antibody detection test has become increasingly important during the last few years as it has been established that for patients with no antibodies detectable in this test, the crossmatch can be abbreviated to one that will detect ABO incompatibility. This can be done with a simple saline suspension of red cells and an incubation of approximately 5 minutes at room temperature. Thus, the approach that has developed involves a careful, thorough, sensitive antibody detection test and then the exact method used for the crossmatch depends on the results of the antibody detection test. If no antibodies are found, the simple rapid test to detect ABO incompatibility is used for the crossmatch.38–40 If antibodies are detected, then the crossmatch uses the longer, more complex methodology used in the antibody detection test.
In the antibody detection test, the patient’s serum is reacted with blood cells specially selected from two normal individuals whose cells contain antigens reactive with all of the common clinically significant antibodies. The conditions of this test usually involve incubation of the patient’s serum and test red cells suspended either in saline or albumin followed by the anti-human globulin test. Other methods to enhance antibody detection that might be used include treating the red cells with enzymes, changing the serum cell ratio, suspending red cells in low ionic strength solution or the use of chemicals such as polybrene to enhance agglutination.41 Gel and solid phase test systems are becoming more widely used.