TRANSFUSION MEDICINE. Table 1 Advantages and Disadvantages of Preoperative Autologous Donation. Directed Donation

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1 X TRANSFUSION MEDICINE Harvey G. Klein, MD* Transfusion medicine has evolved from the empirical administration of blood to a laboratory-based clinical discipline. 1 The discovery of blood group antigens and the understanding of the host immune response to these antigens, the development of methods of anticoagulation and storage of blood, the creation of plastic bags that allow sterile separation of whole blood into components, and the advent of the automated blood cell separator all contributed to its advancement. The potential of blood to act as an agent of disease transmission has heavily shaped both the donation process and transfusion practice. 2 Decisions about whether to transfuse involve weighing the benefits against the risks. This chapter provides a basis for these decisions, including indications for blood-component use, complications of transfusion therapy, and methods of reducing risks during the collection, processing, and preparation of blood components. Therapeutic removal of blood (phlebotomy) and components (apheresis) is also discussed. Blood Donation The donation process for either whole blood or special products, such as single-donor platelets (SDPs) obtained by apheresis, is designed to protect both the donor and the recipient. Donor qualification includes stringent donor screening, physical examination, sensitive testing, donor tracing, and donor deferral when instances of disease transmission are discovered. This system of safeguards has made the US blood supply extremely safe; however, it is not 100% effective. Approximately 2% of volunteer donors still conceal risks that would have led to deferral at the time of donation. 3 autologous and directed donation Autologous donations and directed donations are two strategies adopted by patients seeking to minimize their real or perceived risk of infection from blood components. Autologous Donation and Bloodless Surgery In preoperative autologous donation, patients deposit their own blood, which is then available to them should they need transfusion therapy. Autologous blood avoids the risk of new viral infections and sensitization associated with allogeneic blood; however, it does not eliminate bacterial contamination or the risk of receiving the wrong unit of blood because of clerical error. 4 Absolute contraindications to autologous donation include tight aortic stenosis, unstabl e angina, and active bacterial infection. Anemia and poor venous access frequently limit the number of units that can be collected; up to half of the collected units are not used. With the increasing safety of allogeneic blood, autologous * The author and editors gratefully acknowledge the contributions of the previous author, W. Hallowell Churchill, MD, to the development and writing of this chapter. donation should be limited to selected patients (i.e., those who undergo joint replacement and vascular and cardiothoracic surgery and who are not anemic at the time of the first donation). 5 The advantages and disadvantages of preoperative autologous donation need to be weighed for individual patients [see Table 1]. Acute normovolemic hemodilution (ANH) is another form of autologous donation. In ANH, whole blood is removed from the patient immediately before surgery; the patient is infused with crystalloid solution to maintain normovolemia, and the whole blood that was removed is reinfused when needed, often at the conclusion of surgery. ANH can yield modest blood savings and minimize the risk of clerical error. 6 For patients who experience massive bleeding during surgery, semiautomated collection devices can recover, process, and reinfuse blood lost at the operative site (a process referred to as intraoperative salvage). 6,7 Centers that advertise bloodless surgery combine autologous strategies, erythropoietic support, and conservative transfusion thresholds to limit exposure to allogeneic blood. 8 Directed Donation Blood donated for a specific patient is termed a directed donation; usually, it involves donations made by friends or family members of the intended recipient. Directed donation presumes that the recipient can identify donors who carry lower risk of infections than volunteer donors from the general population. However, prevalence data show that the risk of infectious disease from directed donors is no different from that of first-time donors. 9 The current risk of infection via transfusion is so low [see Table 2] that directed donor programs are justified primarily by patient preferences or by the need for a selected donor serving as the only source of blood components to reduce the recipient s risk from exposure to multiple donors. The latter form of directed donation is most appropriate for neonatal transfusions, in which one of the biologic parents may provide all the needed blood components. 10 In unusual circumstances, such as cases involving highly immunized patients or patients with rare blood types, directed donations from relatives or matched Table 1 Advantages and Disadvantages of Preoperative Autologous Donation Advantages Reduces the risk of transfusion-transmitted infection Prevents immune hemolysis and alloimmunization Prevents many transfusion reactions Provides compatible blood for patients with antibodies Reassures patients and physicians Disadvantages Does not reduce risk of bacterial contamination Carries risk of patient reaction during autologous donation May render patient anemic and iron deficient Costs more than allogeneic donation and half of collected units are unused and discarded 2011 Decker Intellectual Properties 5 hema x transfusion medicine 1 DOI /

2 Table 2 Estimated Risks of Blood Transfusion per Unit Transfused Reaction Risk Comment Fever; allergic reactions 1 in 200 Fever may be > 0.5 C (1 F); allergic reaction may include urticaria Hemolytic transfusion reaction 1 in 6,000 Most are asymptomatic Fatal hemolytic transfusion reaction 1 in 1.8 million Most related to ABO errors HIV infection 1 in 1.9 million HTLV infection 1 in 3 million Hepatitis B infection 1 in 180,000 Hepatitis C infection 1 in 1.6 million Bacterial contamination of platelets 1 in 10,000 Sepsis estimated at 1 in 75,000 Fatalities estimated at 1 in 500,000 Bacterial contamination of red cells 1 in 65,000 Fatality estimated at 1 in 100,000 Transfusion-related acute lung injury 1 in 5,000 Graft versus host disease Uncommon Fatality estimated at 90% HTLV = human T cell lymphotropic virus. unrelated donors are medically indicated. However, the use of blood relatives as donors increases the risk of graft versus host disease, unless the blood is gamma-irradiated. In addition, transfusing a woman of childbearing age with blood from her spouse or her spouse s relatives increases the risk of hemolytic disease of the newborn in subsequent pregnancies. 11 Screening Procedures The combination of improved donor selection and postdonation testing has greatly decreased the infectious risks of allogeneic blood [see Table 2]. Ten screening tests are applied to all donated blood, and supplemental assays, such as testing for cytomegalovirus, are used for special indications, such as stem cell transplantation. postdonation testing Postdonation testing is essential for identifying donors likely to transmit blood-borne infections who are missed in the initial screening process. The risk of transfusiontransmitted viruses is now so low that estimates must be derived from mathematical models rather than from direct measurement of infected blood recipients. 12,13 Screening for Hepatitis Viruses Hepatitis C Screening for hepatitis C began in 1990 with the availability of a serologic enzyme-linked immunosorbent assay (ELISA). The development of ELISAs with improved sensitivity, associated confirmatory tests, and nucleic acid testing (NAT) for viral RNA and DNA has led to a reduction in the per-unit risk of hepatitis C virus (HCV) transmission to less than % (1:1,149,000). 12,13 Before these tests were available, the risk per unit was about 4%. Improved HCV testing has eliminated the need for surrogate tests, such as the measurement of alanine aminotransferase (ALT) levels and testing for antibody to hepatitis B virus (HBV) core antigen (anti-hbc). However, the test for anti-hbc is still used to detect recently infected donors who lack measurable circulating hepatitis B virus surface antigen (HBsAg). 14 The epidemiology of HCV infection is still poorly understood. The majority of transmissions are related to intravenous (IV) drug use. 15 Sexual transmission is uncommon. However, heterosexual transmission of HCV may be asymptomatic and blood donation from a person who was infected with HCV via sexual contact but has not yet developed detectable antibodies is a potential risk to the blood supply. Therefore, persons who are sexual partners of known HCVinfected persons are still excluded from donation. Donors found to be positive for HCV on ELISA should undergo supplemental testing, such as with recombinant immunoblot assays (RIBAs). Donors with positive supplemental test results are likely to have a chronic HCV infection; such persons are rejected as future donors, and they require further clinical evaluation and treatment. 16 Donors with negative supplemental test results probably had false positive screening results and may be eligible for reentry into the allogeneic donor pool after 6 months. The infection status of donors with indeterminate supplemental results is best resolved by testing for HCV RNA; those with only a single band on the most sensitive supplemental test (RIBA-3) have a less than 4% chance of having circulating HCV RNA. 17 Gene amplification methods (NAT) for detecting HCV RNA are used on all blood products before those products are released for transfusion. These tests directly detect the presence of virus before antibody development, and their use is responsible for reducing the risk of HCV transmission to the current minuscule level. Correlation studies have shown that only 80% of samples with confirmed positive results on serologic testing for HCV are also found to be positive on NAT. This finding is consistent with previous estimates of the size of the population of persons who were previously HCV positive but who are no longer infected. Hepatitis B HBV remains a major human pathogen with worldwide distribution that causes acute and chronic 5 hema x transfusion medicine 2

3 hepatitis, cirrhosis, and hepatocellular carcinoma. 18 HBV is highly infectious and is readily transmitted by needle stick and sexual contact. The elimination of the practice of paying whole blood donors together with the development of modern testing methods for HBsAg and anti-hbc has reduced HBV infections to about one in 180,000 units transfused. 19 However, donors with low levels of virus, especially during the incubation period, still transmit disease. HBV immunization of patients requiring multiple transfusions of blood or components has long been advised, and childhood immunization is now standard in the United States. Although vaccination will dramatically reduce the risk of infected donors in the future, breakthrough infections and infections by HBV variants may be a cause for continued vigilance. Hepatitis A Because the viremic phase of hepatitis A virus infection lasts only about 17 days before signs and symptoms develop, hepatitis A transmission from singledonor components is rare. Pooled products, such as factor concentrates, however, carry a substantially higher risk; plasma pools intended for fractionation are screened for hepatitis A. 20 Screening for Retroviruses All donated blood is screened for HIV-1, HIV-2, human T cell lymphotropic virus type I (HTLV-I), and HTLV-II. Data obtained nationally from American Red Cross donors indicate that the HIV infection risk has been reduced from two per 100 transfusions to about one per 2 million transfusions 12 ; improved safety has been achieved by the exclusion of high-risk donors and the postdonation testing for HIV-1 and HIV-2 antibodies and use of NAT for viral RNA or DNA. 12 In follow-up studies, 90 to 95% of recipients of blood that is seropositive for HIV become infected. 21 To have predictive value, the ELISA screening test for HIV must be confirmed by some additional assay such as an alternative ELISA, NAT, or repeated testing on donor review. The possibility of a false positive result should be remembered when one is counseling low-risk donors who have had unexplained positive results on ELISA; these false positive results must always be confirmed by careful clinical follow-up. 22 In the United States, the prevalence of HTLV-I or HTLV-II in donors was about 0.03% in Data from 2001 suggest that the prevalence has been reduced to about 0.01%; about two thirds of these HTLV-positive patients have HTLV-II infection. 12 HTLV is transmitted by cellular components but not by cell-free plasma or plasma derivatives. Infectivity of cellular components declines with the length of refrigerated storage. Several longitudinal studies have defined the clinical consequences of HTLV-I/II infection; they are useful in advising donors who have had positive or indeterminate test results. 23 In a prospective, longitudinal study comparing seropositive blood donors with seronegative blood donors, both viruses were associated with an increase in the incidence of some infectious diseases. No cases of adult T cell leukemia or lymphoma were identified; myelopathies, although rare, were associated with both HTLV types. 24 The risk of HTLV-I/II transmission by blood components is one per 2,993,000. As with HIV, laboratory studies and epidemiologic investigations of HTLV-I/II indicate that patients with positive results on screening tests and negative or indeterminate results on supplemental testing are unlikely to have clinical sequelae; positive results in these patients are most likely false positives. 25 Screening for Other Agents West Nile virus West Nile virus (WNV), a flavivirus imported into the United States in 1999, has become a significant transfusion risk; during periods of epidemics, its transmission rate has been estimated to be 3.02 per 10,000 donations in high-risk metropolitan areas. 26 Approximately 80% of patients are asymptomatic, 20% experience a febrile illness, and about one in 150 develop meningoencephalitis. Elderly and immunosuppressed blood recipients are at particular risk. All blood donations are currently tested for WNV by NAT assays. Several thousand potential transmissions have been interdicted; however, transmissions of WNV continue by means of blood components that have low levels of virus. 27 Chagas disease Chagas disease is caused by infection with the protozoan parasite Trypanosoma cruzi, which is found primarily in Latin America. The risk of severe heart or intestinal complications in infected persons is about 30%; complications usually occur long after the initial infection. Seven cases of transfusion-transmitted T. cruzi and five cases of transmission by organ transplantation have been documented in the United States and Canada, although the mild, nonspecific symptoms of early infection make it likely that many cases have gone unrecognized. A serologic blood screening test has been introduced by the major blood collectors. Whereas follow-up of seropositive donors has not shown evidence of disease transmission, bloodstream parasites are detectable and potentially transmissible decades after immigration, which strengthens the rationale for donor screening. 28 Emerging Infectious Diseases Sensitive and specific testing for known viral agents permits surveillance of the changing prevalence and incidence of pathogens that contaminate the blood supply. 12 Until either screening tests or sterilization procedures become available, exclusions based on demographic considerations are the only possible protective strategy against newly recognized infections. For example, the recognition that WNV was transmitted by blood components prompted the introduction of screening questions to eliminate donors at risk for this disease; however, the screening questions proved largely ineffective. A nucleic acid based test for WNV was introduced in June 2003 and is now a standard screening test for all donated units. 29 In the United Kingdom, another form of demographic control was instituted to safeguard against possible transmission of infectious disease by blood transfusion. The incidence of variant Creutzfeldt-Jakob disease (vcjd), which is the human equivalent of bovine spongiform encephalopathy (mad cow disease), and the concern that vcjd may be transmissible by transfusion prompted in the United States the deferral of donors who had lived in or visited countries in which vcjd was reported; this restriction resulted in a 5 hema x transfusion medicine 3

4 reduction of 4 to 5% in the number of active blood donors. Because no screening assay for vcjd is available and because vcjd infection is uniformly fatal, such epidemiologic precautions were considered warranted. However, transmissibility of vcjd by blood transfusion is likely but has not been proved, and data are inconclusive and limited. 30 Reports from the United Kingdom have identified three probable cases of transfusion-associated vcjd, one subclinical infection in a person who received a transfusion from a vcjd-positive donor, and an infection in a patient with hemophilia that appears to have been transmitted by factor VIII concentrate. 31 In known recipients of blood transfusions from donors who subsequently developed vcjd, the risk of infection is probably high. 31 However, potential blood donors who are rejected on the basis of epidemiologic risk of vcjd should be assured that their risk of having any form of CJD infection is low. A filter designed to remove prions from donated blood is currently undergoing trials. 32 Models have been constructed to predict the emergence of new infectious pathogens, and a listing of known agents with the potential to invade the blood supply has been developed. 31,33 During the past few years, a variety of agents du jour have been proposed as presenting risks for blood transmission, including Chikungunya virus, severe acute respiratory syndrome (SARS) virus, the influenza viruses H1N1 and H5N1, and even the newly described gamma retrovirus XMRV. Other agents, such as Babesia microti (babesiosis) and the malarial parasites, are readily transmitted by transfusion but not easily identified with screening tests. The paradigm of surveillance and testing is gradually being replaced by a strategy of pathogen inactivation of blood components, but it may be decades before all blood components can be rendered safe and effective. Pretransfusion Testing antigen phenotyping Blood recipients are routinely tested to establish their ABO phenotype and Rh type. Establishing ABO type is essential because isoagglutinins (antibodies) against A or B antigens not present on a person s red cells are acquired during the first 2 years of life. These IgM antibodies can cause an immediate hemolytic reaction if ABO-incompatible red cells are transfused. The terminal carbohydrate on these antigens determines specificity in the ABO system, with type A being associated with N-acetylgalactosamine and type B being associated with a terminal galactose. Persons with type O lack both of these terminal sugars. These residues are added by a glycosyltransferase, which was thought to be either nonfunctional or absent in type O persons. Yamamoto and colleagues used molecular techniques to prove that glycosyltransferase in type O persons is very similar to the transferase in type A persons. 34 The type O glycosyltransferase is nonfunctional because of a single base deletion that produces a frameshift and a downstream stop codon. All methods of ABO typing depend on demonstrating that the antigens found on the red cells are consistent with the expected isoagglutinins. D antigen specificity typing in the Rh system is done because of this antigen s potency as an immunogen. Antibodies to the D antigen are the most important cause of isoimmune hemolytic disease of newborns. Rh antigens are membrane glycolipids or glycoproteins. Antibodies against antigens of this class, which includes the Rh, Duffy, Kell, Kidd, and Lutheran systems, will usually cause shortened red cell survival. In contrast to antigens with carbohydrate-mediated specificity, glycolipid and glycoprotein antigens do not stimulate antibody formation unless the transfusion recipient was previously exposed to allogeneic red cells, either from transfusion or from fetal red cells during pregnancy or delivery. D antigen typing is also done using agglutination techniques. In some cases, less antigenic forms of the D antigen, called weak D, require an antiglobulin reagent to enhance detection. Structural studies of the complementary DNA associated with the major Rh antigens (D, Cc, and Ee) have provided probes for direct genotyping. 35 Molecular methods of prenatal Rh-type determination have revealed that most Rh-negative persons lack the D gene. Some persons with the weak D phenotype have mosaic D genes because of exchange with some of the exons of the CcEe gene. Because the genotypes of many of the clinically relevant red cell antigens are known, it is now possible to predict red cell phenotype by DNA analysis. 36 Although DNA analysis for determining red cell phenotype is not yet widely available, it will be useful for recently transfused patients, for whom circulating allogeneic red cells complicate antigen phenotyping. screening for antibodies In addition to identifying patient ABO and D red cell phenotypes, blood banks must screen the patient s serum for red cell specific antibodies, which can cause serious reactions with transfused red cells. Screening involves testing serum against indicator type O red cells displaying all the clinically important red cell antigens. Positive reactions are detected by adding an antiglobulin reagent (i.e., Coombs reagent) to the incubated mixture of type O red cells after it has been washed free of serum. Any observed agglutination is from the reaction of the antiglobulin reagent with antibody adsorbed on the surface of the indicator red cells. Agglutination of the indicator red cells indicates the presence of other antibodies, which require identification. The absence of agglutination excludes all antibodies except those against antigens so rare that they are not displayed on the indicator red cells. Because the alloantibody concentration may fall below the level detectable by agglutination, a negative screen does not guarantee a compatible blood transfusion. Use of type-specific blood removes the risk of ABO incompatibility; however, residual risk of an immunologic reaction from the antibodies to other red cell antigens remains. Such antibodies are present in about 3 to 5% of a random population; they are also present in 10 to 15% of persons who were recently transfused or women with a history of pregnancy. Screening for antibodies reduces the frequency of reactions to about 0.06%. Performing a full crossmatch, in which the recipient s serum is tested against the red cells actually being transfused, is of little additional benefit; a full crossmatch is used primarily to exclude technical errors, confirm ABO compatibility, and detect the rare antibody that is not detected by the screening. 5 hema x transfusion medicine 4

5 Before receiving allogeneic red cells, patients who have had a transfusion or have become pregnant within the past 3 months must be tested for new antibodies every 3 days. For patients not recently exposed to red cells, there is no consensus concerning the appropriate interval between red cell collection and use of the specimen in pretransfusion testing. Commonly, specimens are accepted 14 to 28 days before the date of use. However, one study showed that no new antibodies appeared in paired specimens collected up to 1 year apart, suggesting that a longer acceptance interval may be possible. 37 Blood Components Most blood donations undergo a centrifugal separation process that allows each component to be used for specific indications. Whole blood can be separated into red cells (which contain most of the leukocytes), platelet concentrates (which contain some leukocytes), and plasma. Plasma can be further separated into coagulation components and albumin. Each whole blood unit can potentially support many recipients and clinical needs, maximizing use of each donation. After 24 hours storage, whole blood contains no active platelets, and after 2 days, the labile factors V and VIII are in decline. Therefore, except for some autologous blood programs that use whole blood rather than packed red cells, use of whole blood has now been almost completely supplanted by therapy employing specific blood components. red blood cells The anticoagulant-preservative used determines the shelf life of red cells [see Table 3]. Citrate-phosphate-dextrose (CPD) with the addition of adenine (CPDA-1) increases storage time from 28 to 35 days. Most red cells are now stored in CPD to which extra nutrients have been added, which increases storage time to 42 days. This additive solution sometimes contains additional saline, which can be removed if units with very high hematocrit (approximately 70%) are needed. To prevent febrile transfusion reactions or to delay human leukocyte antigen (HLA) alloimmunization, red cells are further processed by leukocyte reduction (see below) or washing to remove plasma proteins. Current filter technology reduces white cell counts to less than cells per unit, a concentration that is sufficient to reduce febrile transfusion reactions and delay platelet alloimmunization and refractoriness. Washing red cells removes the plasma, leaving less than 0.5 ml per unit, a degree of plasma depletion usually effective in treating allergic transfusion reactions. Washing red cells requires at least 1 hour; it results in a loss of 10 to 15% of cells and usually shortens the product shelf life to 24 hours because breaking the seal on the plastic bag that contains the red cells increases the risk of bacterial contamination. Leukocyte reduction can be accomplished during collection, immediately after collection in the blood bank, or at the bedside during product infusion. Prestorage or laboratory filtration is preferred to bedside filtration. 38 Universal leukoreduction has been implemented in Canada and Europe, but although not required in the United States, it is in widespread (> 70%) use. Freezing is an alternative method for storing red cells. Red cells can be kept in a cryoprotectant (usually glycerol) for 10 years or more. 39 Freezing is therefore ideal for storing rare units or autologous units from persons with rare blood types, for whom it is difficult to find compatible allogeneic red cells. When a unit is at the end of its liquid storage shelf life, the cells can be rejuvenated with fresh media and nutrients; they can then be refrozen and stored. To be used, frozen red cells must be thawed and the glycerol removed; Product Table 3 Characteristics of Blood Products and Indications for Use Volume (One Unit) Hct or Platelet Count Whole blood ml Hct 35 45% g Hb Red cells ml Hct 55 70% g Hb Shelf Life days, depending on preservative Same as whole blood Donors per Unit Storage outside Blood Bank Indication C Massive transfusion, exchange transfusion for newborn younger than 3 days C To increase oxygen-carrying capacity for anemic or bleeding patients Washed red cells 250 ml Hct 55 70% 24 hr C Allergies to plasma proteins Frozen deglycerolized red cells Platelet concentrates whole blood derived Single-donor (apheresis) platelets Hb = hemoglobin; Hct = hematocrit ml Hct 35 45% 10 yr frozen; 14 days thawed 40 ml days 1/U given as 4 6 U pool ml Hct < 1% 3 5 ml C Autologous blood; long-term storage of rare units; supplement to refrigerated inventory; prevention of anaphylactic reaction to plasma proteins C For major bleeding or surgical procedures when platelet count < 50, ,000/µL; for bleeding prophylaxis when platelet count < 10,000/µL 5 days C Same as for platelet concentrates, but preferred because of fewer donor exposures 5 hema x transfusion medicine 5

6 consequently, the product is expensive and preparation time is longer than for products stored in the liquid state. platelets Platelets can be provided either as platelet concentrates from a number of blood donors or from a single donor [see Table 3]. SDPs are collected by a continuous apheresis process that removes platelets and returns all other blood components. A single transfusion of platelet concentrates usually consists of platelets derived from four to six units of donated whole blood, which is about the same number of platelets contained in one SDP product. Platelets are suspended in 200 to 300 ml of plasma. The advantage of SDP therapy is the reduced risk of blood-borne infection and antigen exposure because the product is from one donor rather than from four to six; the disadvantages are a longer collection time, greater cost, and, often, limited supply. 40 ABO Rh compatible platelets should be used when possible because significantly better therapeutic results are obtained from compatible transfusions. 12,41 plasma Fresh frozen plasma (FFP), which is plasma that is frozen within 8 hours of collection, contains all the procoagulants at normal plasma concentrations. Units of FFP prepared from whole blood generally contain 300 to 330 ml and virtually all plasma proteins in concentrations equivalent to those of fresh plasma. After thawing, FFP can be kept for 24 hours at 1 to 6 C and will retain 3 to 4 mg/ml of fibrinogen and 1 IU/mL of the other clinically important coagulation proteins. Plasma stored for up to 24 hours before freezing (FP-24) is considered equivalent to FFP for all intents and purposes. Cryoprecipitate consists of the cryoproteins recovered from FFP when it is rapidly frozen and then allowed to thaw at 2 to 6 C. These cryoproteins include fibrinogen, factor VIII, von Willebrand factor, factor XIII, and fibronectin. About 40% of the components in FFP are recovered. The cryoproteins are suspended in a small amount of plasma that contains ABO isoagglutinin at the concentration found in normal plasma. A pool of 10 units of cryoprecipitate (each derived from one unit of FFP) contains an amount of fibrinogen equivalent to four units of FFP but in one fourth to one fifth the volume. Consequently, a cryoprecipitate pool permits more rapid replacement of fibrinogen than FFP but has the disadvantage of more donor exposures. After the cryoprecipitate is removed from FFP, the residual product is known as cryopoor plasma. Once frozen, cryopoor plasma has the same shelf life as FFP [see Table 4 and Table 5]. With the exception of a few cell-associated pathogens, such as HTLV I/II and malarial parasites, plasma components present the same risk of infectious disease transmission as does whole blood. Transfusion of Red Cells indications for allogeneic transfusion Acute Blood Loss The decision whether to use red cells depends on the etiology and duration of the anemia, the rate of change of the anemia, and assessment of the patient s ability to compensate for the diminished capacity to carry oxygen that results from the decrease in red cell mass. 42 Management of acute anemia caused by bleeding or operative blood loss will differ from management of chronic anemia to which the patient has adapted. However, the question underlying any red cell transfusion is whether there is sufficient oxygen delivery to tissues for current needs. Compensatory mechanisms for acute blood loss include adrenergic response, leading to constriction of venous beds, which improves venous return; increased stroke volume, tachycardia, or both; and increased peripheral resistance, which eventually redistributes blood flow to essential organs. Also contributing to the maintenance of intravascular volume is the shifting of fluid to the intravascular space; this shifting occurs relatively rapidly from the extravascular space and more slowly from the intracellular to the extravascular space. A decrease in blood volume has distinct effects on oxygen delivery, depending on the volume of blood lost and the functioning of the compensatory cardiovascular responses. Restoration of intravascular volume, usually with crystalloid, ensures adequate perfusion of peripheral tissue and is the first treatment goal for a patient with acute blood loss. Whether red cell transfusion is required depends on the extent of blood loss and the presence of comorbid conditions that may limit host response to the blood loss. The American College of Surgeons has correlated blood loss with clinical findings. Loss of up to 15% of total blood volume (class I hemorrhage) usually has little effect; this amount is the maximum permitted in normal blood donation. A class II hemorrhage (15 to 30% loss) results in tachycardia, decreased pulse pressure, and, possibly, restlessness. A class III hemorrhage (30 to 40% loss) leads to obvious signs of hypovolemia; mental status often remains normal. Red cell transfusion is usually indicated when blood loss exceeds 30% in a patient without other significant comorbid conditions. However, the presence of serious cardiac, peripheral vascular, or pulmonary disease can lower this threshold. For example, anemic patients with significant coronary artery disease are more likely to have serious postoperative myocardial complications. One unit of red cells will raise the hemoglobin concentration about 1 g/dl in an adult. The threshold for red cell transfusion has been evaluated in two randomized, controlled trials. In one study of transfusion after coronary artery bypass, patients who received transfusions for hemoglobin levels below 8 g/dl did no worse than patients who received transfusions for hemoglobin levels below 9 g/dl. 43 The other trial compared outcomes in critical care patients who received transfusions when their hemoglobin level fell below either 7 or 10 g/dl. 44 Enrolment in this study was limited to patients who were euvolemic at entry and whose hemoglobin levels were from 7 to 9 g/dl; patients who had undergone routine cardiac procedures or who were actively bleeding on entry to the intensive care unit were excluded. There was no statistical difference in 30-day mortality for these two groups. However, in the subgroups of patients younger than 55 years and patients whose illness was less severe, as defined by standardized clinical criteria, Kaplan-Meier survival estimates were significantly better in the patients 5 hema x transfusion medicine 6

7 Component Fresh frozen plasma Cryoprecipitate Recombinant factor VIIa (rfviia) Factor VIII concentrate Recombinant factor VIII Factor IX concentrate Table 4 Plasma and Recombinant Clotting Factors Volume (One Unit) Shelf Life Donors per Unit ml 1 yr frozen; 24 hr thawed ml; pool of U = 200 ml 1 yr frozen; 24 hr thawed Storage outside Blood Bank Indication C Multiple coagulation factor deficiency from bleeding or DIC; reversal of warfarin therapy; factor XI deficiency; treatment of TTP 1/U; given as a pool of U 2 6 C 4 10 ml Per label None 2 8 C; up to 3 hr at room temperature, after reconstitution 5 20 ml 2 8 C for up to 2 yr; at room temperature for up to 2 mo Up to 60,000 per batch; filtered and treated to reduce risk of pathogen transmission Room temperature for up to 2 mo ml Per label None 2 8 C or at room temperature for up to 3 mo 5 20 ml 2 8 C for up to 2 yr; room temperature for up to 2 mo Up to 60,000 per batch; filtered and treated to reduce risk of pathogen transmission Room temperature for up to 2 mo Replacement of fibrinogen or abnormal fibrinogen; replacement of von Willebrand factor, if concentrate unavailable; replacement of factor XIII See Table 5 Congenital factor VIII deficiency (hemophilia A) Congenital factor VIII deficiency (hemophilia A) Congenital factor IX deficiency (hemophilia B) DIC = disseminated intravascular coagulation; TTP = thrombotic thrombocytopenic purpura. who were not transfused unless hemoglobin levels dropped below 7 g/dl. These results are provocative, but they must be interpreted cautiously. 45 They do suggest that more restrictive transfusion policies may be safely adopted for selected patients. However, the enrolment criteria may have biased the findings, and this calls into question the applicability of these findings to other settings. Chronic Anemia In the chronically anemic patient, an increase in red cell 2,3-diphosphoglycerate leads to a shift in the oxygen dissociation curve and improved delivery of oxygen to tissues. This adaptation augments the mechanisms for improved oxygen delivery described above. Indications for transfusion depend on clinical assessment of the adequacy of oxygen Table 5 Recombinant Factor VII Indications and Dose Indication Dose Comment Approved indications Treatment or prevention of bleeding in hemophilia patients with inhibitors to factor VIII or IX Treatment or prevention of bleeding for congenital factor VII deficiency Off-label use 90 µg/kg q. 2 3 hr; minimal effective dose not established µg/kg q. 4 6 hr; minimal effective dose not established Treatment indicated for rapid bleeding or bleeding in a critical site; as preventive measure, used before invasive procedure Dose and frequency adjusted for individual patients Intracerebral hemorrhage (except subarachnoid) µg/kg Treatment within 4 hr of onset of bleeding limits hematoma growth, reduces mortality, and improves function at 90 days Rapid reversal of anticoagulant therapy Dysfunctional platelets and life-threatening hemorrhage Uncontrolled bleeding in patients with trauma and hepatic failure or during surgical or obstetric procedures DDAVP = 1-desamino-8-d-arginine vasopressin (desmopressin). 90 µg/kg; minimal effective dose not established µg/kg; dose titrated to maintain hemostasis µg/kg; minimal effective dosage not established Used to reverse effects of warfarin and Xa inhibitors Used when coagulopathy is not corrected by platelets or DDAVP Rescue therapy after component therapy fails; repeated dosing as necessary to achieve hemostasis 5 hema x transfusion medicine 7

8 delivery and are also guided by the etiology of the anemia. 42 In patients for whom the anemia can be reversed with iron, folic acid, or vitamin B 12, transfusion therapy is indicated only when clinical conditions cannot be tolerated during the period in which the endogenous red cell mass is being regenerated. Patients with chronic renal disease are typically deficient in erythropoietin. Replacement therapy with exogenous erythropoietin often obviates transfusion. It is rarely necessary to return the hematocrit to normal levels to provide safe, clinically effective therapy. 46 Patients with anemia that is a result of chronic disease such as rheumatoid arthritis, chemotherapy for malignancy, myelodysplasia, or AIDS may also respond to erythropoietin, but caveats regarding the rate of hemoglobin elevation and the tolerable hemoglobin concentration remain. 47 Relatively little is known about transfusion thresholds in specific medical illnesses. Observational analyses have suggested that the transfusion trigger should be more liberal for patients with cardiovascular disease and that correction of anemia improves mortality in elderly patients hospitalized with myocardial infarction and for patients with congestive heart failure. No single laboratory measurement or combination of physiologic markers predicts the need for red cell transfusion; the decision to transfuse red cells continues to rely on evaluation of the individual patient by skilled clinicians at the bedside who use hemoglobin concentration as no more than a helpful guide. 42 indications for autologous transfusion Whether the criteria for autologous transfusion should be the same as that for allogeneic transfusion remains unresolved. Although the risk associated with autologous blood is less than that associated with allogeneic blood, it is not zero. Errors in labeling, storage, and processing can still occur. For these reasons, many argue that uniform standards based on oxygen delivery should apply, regardless of the blood source. Others, citing the reduced risk, advocate returning most or all of the predeposited units to the patient. There is no clinical evidence that either transfusion policy is associated with better or worse patient outcomes. Transfusion of Platelets In general, the decision to transfuse platelets rests on the answers to two questions: (1) Is thrombocytopenia the result of underproduction or increased consumption of platelets? and (2) Do the existing platelets function normally? indications for transfusion Low Platelet Count Thrombocytopenia can result from decreased production caused by marrow hypoplasia or from increased consumption caused by conditions such as disseminated intravascular coagulation (DIC) or a combination of both as in immune thrombocytopenic purpura (ITP). 48 In a patient with ITP, surviving platelets are larger and younger and function better than would be expected given the platelet count; platelet transfusion is largely avoided or minimized for such a patient, although in life-threatening situations, the transient increment from a platelet transfusion can prove vital. In contrast, with hypoplasia, hemostasis is more severely impaired, and the risk of bleeding is relatively higher. Platelet transfusions should be given to patients with clinically significant hemorrhage and severe thrombocytopenia. The decision to transfuse patients who have hypoproliferative thrombocytopenia prophylactically is generally initiated when the platelet count drops below a certain threshold. Published consensus guidelines provide an excellent summary of all aspects of platelet therapy. 49 The time-honored transfusion threshold of 20,000/µL used for platelet prophylaxis was established on the basis of studies of patients receiving aspirin; the results of more recent controlled trials indicate that this threshold is high. The prevalence of bleeding increases significantly below a threshold of about 10,000 platelets/µl in otherwise asymptomatic patients. 50 Transfusion at levels above 10,000 platelets/µl may be necessary in newborns; in patients with signs of hemorrhage, high fever, precipitous decline in platelet count, and additional hemostatic defects; and in patients undergoing invasive procedures. 49 Dysfunctional Platelets Platelet function is the second criterion for the transfusion of platelets. Transfusion is appropriate in a bleeding patient whose platelet count is adequate but whose platelets are dysfunctional as a result of medications such as aspirin or thienopyridines or as a result of bypass surgery. In a bleeding patient, if platelet dysfunction is the result of inherited or acquired defects, transfusion is indicated to provide a minimum number of normal platelets. Platelet function is abnormal in uremic patients, and definitive treatment requires correction of the uremia. Some studies suggest that interventions that increase von Willebrand factor levels, such as desmopressin (1-desamino-8-d-arginine vasopressin [DDAVP]), conjugated estrogen, or cryoprecipitate, may favorably influence platelet function in uremia. 44 In vitro evidence suggests that DDAVP may improve platelet dysfunction caused by glycoprotein IIb or glycoprotein IIIa (GPIIb/IIIa) inhibitors (e.g., eptifibatide, abciximab, tirofiban) or aspirin. 49 contraindications to platelet transfusion Proper investigation of the causes of thrombocytopenia will identify clinical situations in which platelets are traditionally withheld because they may contribute to the evolution of the illness. These disorders include thrombotic microangiopathies, such as thrombotic thrombocytopenic purpura (TTP), hemolytic-uremic syndrome, and HELLP syndrome (hemolysis, elevated liver enzymes, and a low platelet count). Patients with these disorders rarely bleed; when hemorrhage occurs, platelet transfusion may prove lifesaving. Posttransfusion purpura is usually unresponsive to platelet transfusions that are not matched to avoid the platelet-specific antigen, but it may respond to intravenous immune globulin (IVIg) or plasma exchange. Transfused platelets are short-lived in patients with immune thrombocytopenia (e.g., ITP), but they cause no harm and may effect hemostasis temporarily when hemorrhage occurs. Platelet infusions should be considered in high-risk patients with ITP, such as children with bleeding signs beyond petechiae and purpura who may be at particular danger of intercranial hemorrhage hema x transfusion medicine 8

9 response to platelet transfusions Both platelet and host factors influence the response to platelet transfusions. Length of in vitro storage, storage temperature, adequacy of oxygenation, and extent of pretransfusion manipulation all influence in vivo survival. Important host factors that influence survival are body temperature, underlying disease, splenomegaly, ABO compatibility, and immune status. A transfusion of appropriately stored fresh platelets whether pooled concentrates or SDPs should contain about 6,000 to 10,000/µL platelets per unit ( platelets). Thus, in an unsensitized 75 kg (165 lb) recipient, each unit should yield an increment of about 60,000 platelets/µl. A posttransfusion count is usually obtained after 1 hour; however, a count can be obtained as early as 10 minutes after transfusion. Smaller doses of prophylactic platelet transfusions result in a decreased number of platelets transfused per patient and no effect on the incidence of bleeding but an increased number of transfusions. 52 A case is considered refractory to platelet transfusions when the 1-hour posttransfusion increment is less than 10,000 platelets/µl after the patient is given freshly stored (< 48 hours) platelets. platelet transfusions in refractory cases There is no evidence that repeated administration of platelet concentrates in the absence of a measurable increment improves hemostasis. Poor response (refractoriness) to platelets may be either immune or nonimmune. Platelets express platelet-specific antigens, HLAs, and blood group antigens. Immune response to any of these can contribute to platelet unresponsiveness. Platelet surfaces have only class I HLA antigens, of which only HLA-A and HLA-B are clinically important. Polymorphic antigens are found in association with each of the major platelet proteins: HPA1a/2a (formerly called Pl A1/A2 ) and HPA4 (Pen) on glycoprotein IIIa, HPA3a/b (Bak system) on glycoprotein IIb, and HPA 2a/b (Sib and Ko) on glycoproteins Ia and Ib. Each of these antigen groups is associated with isoimmune neonatal thrombocytopenia. The prevalence of antibodies to platelet-specific antigens is increased for patients sensitized to HLA antibodies; therefore, antibodies to both sets of epitopes may contribute to refractoriness in patients who fail to respond to HLA-matched platelets. 53 For patients who are refractory to platelet transfusions, treatment involves addressing nonimmune causes (e.g., fever, sepsis, bleeding, and DIC) and providing recently collected ABO-compatible components. If these strategies fail, minimization of the effects of HLA antibodies or platelet antigens through HLA typing, platelet crossmatching, or both is indicated. 48,52 Selecting platelets matched at the HLA-A and HLA-B loci may improve responsiveness in about half of patients with positive HLA antibody screens. Computed best-match selection programs prove useful when identical matches are unavailable. 54 Unless contraindicated because of transplant considerations, an empirical trial of donations from family members may also be helpful. Platelets can be selected for alloimmunized patients by HLA matching or by platelet crossmatching. If a patient has a high titer antibody to a specific HLA antigen, platelets lacking the cognate antibody can be selected. Otherwise, closely HLA-matched platelet preparations provide the best chance of an effective transfusion. Crossmatched platelets provide equivalent platelet increments that may be independent of the grade of HLA match. 55 Although these results are promising, the effectiveness of selection either by HLA and crossmatching or by crossmatching alone is often limited by nonimmune host factors. Modifying the effects of alloimmunization is difficult. IVIg can improve platelet increments but not platelet survival. In some circumstances, response reflects an underlying autoantibody in addition to alloantibodies. Plasma exchange is of limited value because it is difficult to remove IgG antibodies. In some patients, the HLA antibodies responsible for refractoriness may regress over time; it is therefore important to periodically retest for the presence of HLA antibodies. If the HLA antibody screen becomes negative, a trial of non HLA-matched (i.e., from random donors) platelets is warranted. All in all, the best strategy is prevention, which can be achieved by avoiding unnecessary transfusions and using only leukocyte-depleted components. A randomized, prospective trial examined how best to prevent alloimmunization in newly diagnosed patients with acute myeloid leukemia. The study compared leukocyte reduction by filtration and by ultraviolet B irradiation of platelets; both methods were equally effective. 56 In addition, the study found that platelets obtained from single random donors provided no additional benefit over pooled platelet concentrates from random donors. 56 Although leukocyte reduction significantly reduced the occurrence of alloimmunization, it did not prevent secondary immune responses in patients already sensitized through either pregnancy or transfusion. 56,57 Transfusion of Fresh Frozen Plasma, Plasma Derivatives, and Recombinant Products fresh frozen plasma Despite a paucity of indications for FFP use, roughly 4 million units are transfused annually. 12,41,58 FFP is most appropriate for replacing the multiple coagulation deficiencies that result from massive transfusion, liver disease, warfarin toxicity, or acute or chronic DIC. In addition, FFP can be used to treat thrombotic microangiopathies and specific factor deficiencies when factor concentrates are not available. 59 After one blood volume exchange using only red cells, plasma components are diluted to about 40% of their original concentration; after two blood volume exchanges, plasma components are diluted to 15%. Prothrombin time (PT) and partial thromboplastin time (PTT) become prolonged when coagulation components are lower than 30%, but abnormal bleeding from dilution usually does not occur until these values are less than 17% of normal. Microvascular bleeding associated with a PT and a PTT greater than 1.5 times normal is an indication for FFP. Whether FFP replacement is needed when PT and PTT are over 1.5 times normal but are not associated with bleeding is less clear-cut; paracentesis and thoracentesis did not cause increased bleeding in patients with PT and PTT that were up to twice 5 hema x transfusion medicine 9