ABO forward typing is the process in which red blood cells are mixed with a known antibody (anti-A or anti-B). This process identifies the antigens present on the red blood cells by the visually apparent agglutination of the cells when an antibody combines with the corresponding antigen (e.g., anti-A with antigen A).

ABO reverse typing tests serum for the presence of predicted ABO antibodies by adding red blood cells of a known ABO type.

The Rh factor is the red cell antigen D. Rh typing is accomplished by testing red cells against anti-D serum. If agglutination occurs, the red cells possess the D antigen and the blood is Rh positive. Some people demonstrate a weak expression of the D antigen (formerly referred to as D ^U). In the past, laboratory testing to identify this weak D antigen included the indirect antiglobulin test. However, that test is no longer necessary in most cases because licensed anti-D reagents are sufficiently potent to identify patients with a weak expression of the D antigen as Rh positive. These individuals are considered Rh positive as donors and recipients.

Additional testing for red cell antigens is not recommended or encouraged by the AABB, formerly known as the American Association of Blood Banks.

Unexpected antibodies are those other than anti-A or anti-B. Many blood banks screen all donated units for clinically significant antibodies rather than limiting their search to the donor group most likely to harbor them. The most likely donors of blood with unexpected antibodies are those with a history of pregnancy or previous transfusion. In general, clinically significant antibodies are those known to have caused hemolytic disease of the newborn, a frank hemolytic transfusion reaction, or unacceptably short survival of transfused red blood cells (Roback et al, 2008).

All donor blood must be tested to detect units that might transmit disease (Klein and Anstee, 2005). Components and whole blood units must not be used for transfusion unless all tests are nonreactive, are negative, or have values within normal limits.

The following is a brief summary of the substances that preserve blood:

Red cells that have been stored up to 3 days beyond their expiration dates can be incubated (at 37° C for 1 hour) in FDA-approved solutions containing inosine, pyruvate, phosphate, adenine, and sometimes glucose. This incubation will increase the cellular levels of ATP and 2,3-diphosphoglycerate (2,3-DPG). These rejuvenated cells may be washed and used within 24 hours, or they may be glycerolized and frozen for extended storage (Roback et al, 2008).

There are four blood types in the ABO system: A, B, AB, and O. The name of the blood type is determined by the name of the antigen on the red cell. The type of antigen present on the red cell is an inherited characteristic; the A and B genes are equally dominant, and the O gene is recessive (Table 14-3).

The A and B genes dictate the presence of A and B antigenic determinant sites, respectively. Although the O gene is inactive and does not code for any of the erythrocyte alloantigens, blood group O erythrocytes do exhibit an antigenic glycoprotein on their surface—the H antigen. This glycoprotein is not the product of the O gene, as evidenced by its presence on red blood cells of all types.

The relationship between the A, B, and H antigens can be explained as follows. During the synthesis of the blood group molecules, the H antigen is synthesized first; thus the H antigen is present on all red cells. If the A gene is present, it will code for a transferase (enzyme), which will facilitate the attachment of the sugar N-acetylgalactosamine to the H antigen. This chemical complex is the antigenic determinant for blood group A. Similarly, the B gene will code for a different transferase that will allow for the attachment of an alternate sugar group, d-galactose, which will complete the antigenic determinant for blood type B. Group O individuals do not possess either enzyme system, and thus group O erythrocytes possess only the unmodified H antigen on their surface (Smith, 2001 and Roback et al, 2008). The antibodies of the ABO system occur naturally (i.e., without direct antigen stimulation) and are called isohemagglutinins. They are complete, and in the presence of red cells that exhibit the corresponding antigen; they can cause agglutination in a 0.9% sodium chloride medium. The antibody that agglutinates type A is called antibody A (anti-A), and the corresponding antibody for antigen B is called antibody B (anti-B).

This adversarial relationship between antigen and the corresponding antibody is the basis for understanding compatibilities within the ABO system. The antigens are located on the cells, and the antibodies reside in the plasma. If a unit of red cells is to be administered it should be thought of as an antigen and should be given only to a recipient who does not exhibit the corresponding antibody. Conversely, plasma should not be given to a recipient who possesses the corresponding red cell antigen (Table 14-4).

The Rh system is complex and extensive. Because nearly 50 Rh antigens have been identified, a complete discussion of this system is not included here. Sufficient for the topic of routine transfusion therapy are the unmodified terms of Rh+ (Rh positive) and Rh− (Rh negative), which respectively refer to the presence or absence of the red cell antigen D.

The blood recipient who carries antigen D (Rh positive) may receive products that are either Rh+ or Rh−. However, a recipient who is Rh negative should receive only blood products that are Rh negative. This is especially true for Rh-negative women of childbearing age who might become sensitized to the D antigen, which could raise the potential for complications in subsequent pregnancies.

The HLA blood grouping system consists of a series of highly immunogenic antigens that can be found predominantly on the cells of the leukocyte family. These antigens exist on the surface of the lymphocytes, granulocytes, monocytes, and platelets. Although the HLA antigens and their precipitated antibodies are best known for their role in transplantation rejection, they also contribute to several of the complications of transfusion therapy, including the following:

Whole blood requires no processing beyond collection into an anticoagulated closed collection system and testing. It is stored at 1° to 6° C with the satellite pack attached. If packed cells are needed at any time during the shelf life of the blood, this satellite pack will allow for their separation within a closed system. However, because whole blood transfusions are rarely used except to treat massive blood loss, most homologous donations are not stored as whole blood but are separated into components soon after donation. Autologous donations, which are planned to be transfused back to the donor within the shelf life period for refrigerated blood, are stored whole. These units are often given as whole blood. They can be spun down and given as packed cells if the donor-recipient does not need or cannot tolerate the additional volume that the plasma represents.

Clinical applications for the administration of whole blood include the following:

Although whole blood may be appropriate for the preceding clinical situations, it is not always readily available. Therefore the use of packed red cells in combination with asanguineous solutions has become the standard when replacement therapy is needed in surgery or trauma cases (Klein, Spahn, and Carson, 2007 and Roback et al, 2008).

Packed red blood cells are prepared by separating the plasma from the cellular portion of a unit of whole blood. This can be done any time before the expiration date. Cells can be separated from plasma by centrifuge, which causes a rapid separation, or by sedimentation, in which cells will settle to the bottom of an upright container and the plasma will concentrate on top. Once separation has occurred, 200 to 250 mL of plasma can be manually expressed into the attached satellite bag.

The shelf life of a unit of packed red blood cells (PRBCs) is the same as that for the unit of whole blood from which it was obtained, but it can be extended if an additive system is mixed with the cells at the time of their separation (see previous discussion under Anticoagulants and Preservatives). These additive solutions, which must be added within 72 hours of the blood donation, extend the shelf life of the packed cells from 35 to 42 days.

PRBCs are used for routine blood replacement during surgery and to increase the oxygen-carrying capacity (i.e., the red blood cell mass) in patients with symptomatic anemia that cannot be treated with pharmaceuticals.

Granulocytes are usually prepared by leukopheresis. This blood component also contains other leukocytes, platelets, and some red cells in 200 to 300 mL of plasma. They should be transfused as soon as possible after collection but may be stored at 20° to 24° C without agitation for up to 24 hours (Roback et al, 2008).

The use of granulocyte transfusion in adults is rare. When this therapy is used, the recipient is usually severely neutropenic with documented infection that is unresponsive to aggressive antibiotic therapy. The candidate for granulocyte transfusion should meet the following three conditions:

In the pediatric population, granulocyte transfusion has been used in conjunction with antibiotic therapy for severe bacterial neonatal sepsis. Although controversy surrounds this choice of therapy, there appear to be clinical situations in which granulocyte transfusion can supplement antibiotics. The AABB (Roback et al, 2008) states that pediatric candidates for granulocyte transfusion are infants with all of the following conditions:

Granulocytes should come from CMV-negative donors because they cannot be given though a leukocyte filter to reduce the risk of CMV transmission. Granulocytes should also be irradiated to reduce the risk of GVHD.

Fresh-frozen plasma (FFP) is prepared by removing the plasma from a unit of whole blood and freezing it within 6 hours of collection. The storage time for FFP is 1 year at 18° C or colder. This component, if kept frozen and then thawed in a warm water bath (30° to 37° C) just before use, is an excellent source of all clotting factors, including the labile factors V and VIII and fibrinogen. The activity of these labile factors is lost when plasma is stored in the nonfrozen state (Roback et al, 2008).

FFP is indicated when clotting factors are needed for which a concentrate is not available, in the presence of severe liver disease where limited synthesis of plasma coagulation factors may be suspected, and when needed to counteract the effects of warfarin therapy (Box 14-1).

Administering a blood component is the last step in the process of matching a donor component with a recipient. Remembering that the most common causes of fatal transfusion reactions are improperly labeled blood samples, mislabeled component units, and misidentified recipients, it is clear that most fatal transfusion errors are clerical rather than laboratory failures. The transfusionist is the last person in the administration process with the opportunity to note a clerical error. Therefore the transfusionist should be attentive to every detail of the administration procedure and guard against the relaxed approach that so often accompanies familiarity.

Policies and procedures for the administration of blood components vary greatly among providers of this therapy, but their purpose, which is to ensure precision and safety, is universal (Box 14-3). Therefore those who administer transfusion therapy should be knowledgeable of policy and adhere strictly to the procedures embraced by their particular organization or home care provider.