Comprehensive Study Guide on Blood Components and Transfusion Medicine

Fundamental Concepts of Blood and Blood Products as Therapeutic Agents

Blood and various blood products are formally considered to be drugs. They are utilized extensively in the treatment of diverse diseases, although clinicians must remain vigilant as adverse effects may occur during or after administration. Notably, the transfusion of blood cells is fundamentally a form of transplantation, which carries complex immunological implications for the recipient.

Methodologies of Blood Component Collection: Apheresis and Hemapheresis

Apheresis, also known as hemapheresis, defines a specific method of blood collection. In this process, whole blood is withdrawn from a donor, a desired component is separated for collection, and the remaining components of the blood are subsequently returned to the donor's circulation. There are two primary mechanical methods used to achieve this separation: Intermittent-Flow Centrifugation (IFC) and Continuous-Flow Centrifugation (CFC). Intermittent-Flow Centrifugation requires only a single venipuncture. During IFC, blood is withdrawn and eventually reinfused through the same needle; once the target component is separated, the remaining contents are reinfused, completing one cycle. Conversely, Continuous-Flow Centrifugation processes the blood simultaneously, with withdrawal and return occurring at the same time. This methodology necessitates two separate venipuncture sites on the donor.

Donor Selection Criteria and Plasmapheresis Monitoring

Specific physical criteria are established for blood donors to ensure safety and product quality. For male donors, the minimum requirements include a weight of at least $130\,lbs$, a height of at least \text{5'1''}, and a hematocrit of at least $40\%$. Female donors must meet a weight requirement of at least $150\,lbs$, a height of at least \text{5'5''}, and a hematocrit of at least $40\%$. These values are essential for maintaining donor health during the collection process.

Frequent plasma donors are subject to additional medical oversight. They must maintain a total serum protein level of at least $6.0\,g/dL$, which is verified before every donation. Furthermore, these donors are required to undergo serum protein electrophoresis or quantitative immunodiffusion every $4\,months$, in addition to receiving an annual physical examination conducted by a licensed physician.

Structural Integrity of Collection Systems: Closed versus Open Systems

Blood collection systems are categorized as either closed or open, with significant implications for sterility and storage. A closed system maintains sterility throughout the process by using attached satellite bags or a sterile connecting device that welds tubing from one bag to another without air exposure. Due to this preserved sterility, there is no change to the component's original storage effect. In contrast, an open system occurs when the seal on the unit is broken to attach an external transfer bag. This exposure to air poses a substantial threat of bacterial contamination. Consequently, components stored at temperatures between $1\,^\circ C$ and $6\,^\circ C$ must be used within $24\,hours$ after the system is opened, while components stored at $20\,^\circ C$ to $24\,^\circ C$ must be utilized within $4\,hours$.

Mechanical Processing and Component Separation from Whole Blood

The preparation of blood components involves distinct physical processes starting from whole blood. Red Blood Cells (RBCs) are prepared through leukoreduction filtration, centrifugation, or apheresis. Platelets are derived through in-line filtration, centrifugation, or apheresis. Fresh Frozen Plasma (FFP) is produced by heavy spin centrifugation followed by freezing at temperatures of $-18\,^\circ C$ or colder. Cryoprecipitate is created via the slow thawing of frozen plasma to collect the cryoprecipitated antihemophilic factor. Granulocytes are typically collected via apheresis.

The process often utilizes a soft or light spin initially to separate whole blood into Packed RBCs and Platelet Rich Plasma (PRP). The PRP can then undergo a hard spin to produce Platelet Poor Plasma (PPP) and Platelet concentrate. Plasma can be further frozen within specified timeframes to create Fresh Frozen Plasma, which is maintained at $-18\,^\circ C$ or colder.

Standard and Specialized Red Blood Cell Components

Whole blood is indicated primarily for expanding blood volume and providing RBC mass in cases of acute blood loss. It is stored between $1\,^\circ C$ and $6\,^\circ C$ and transported between $1\,^\circ C$ and $10\,^\circ C$. The shelf-life depends on the anticoagulant used: $21\,days$ for Acid-Citrate-Dextrose (ACD) and Citrate-Phosphate-Dextrose (CPD), and $35\,days$ for Citrate-Phosphate-Dextrose-Adenine (CPDA-1). Packed RBCs are used to increase the RBC mass in symptomatic normovolemic patients. Their shelf-life matches whole blood in a closed system but is limited to $24\,hours$ in an open system.

Leukocyte-reduced RBCs are specifically indicated for patients experiencing severe or recurrent febrile transfusion reactions due to leukocyte antibodies, or those at risk for Human Leukocyte Antigen (HLA) alloimmunization or Cytomegalovirus (CMV) susceptibility. In this product, the absolute White Blood Cell (WBC) count must be reduced to less than $5 \times 10^6$ while maintaining at least $85\%$ of the original RBC mass. Storage and shelf-life parameters align with standard RBCs. Washed RBCs are indicated for symptomatic anemic patients with a history of allergic, febrile, urticarial, or anaphylactic reactions. Once washed, these units have a strict shelf-life of $24\,hours$.

Cryopreservation of Red Blood Cells

Frozen RBCs are reserved for the long-term storage of rare blood types or autologous units. They are stored at $-65\,^\circ C$ or $-120\,^\circ C$ and can be kept for up to $10\,years$. Once deglycerolized, they have a shelf-life of $24\,hours$ unless a closed system was used. Quality control procedures for these units ensure an RBC recovery of at least $80\%$, good viability, and a residual intracellular glycerol level of less than $1\%$.

There are three primary methods for freezing red cells. The high glycerol method freezes at $-80\,^\circ C$ and stores at $-65\,^\circ C$. The low glycerol method freezes at $-196\,^\circ C$ and stores at $-120\,^\circ C$. The agglomeration method freezes at $-80\,^\circ C$ and stores at $-65\,^\circ C$.

Platelet Concentrates

Platelet concentrates can be derived from whole blood (Random Donor Platelets, RDP) or via plateletpheresis (Single Donor Platelets, SDP). A single unit of RDP contains approximately $5.5 \times 10^{10}$ platelets and is expected to increase the recipient's count by $5,000$ to $10,000/\mu L$. APheresis units contain a much higher count of $3.0 \times 10^{11}$ platelets, leading to an expected increase of $30,000$ to $60,000/\mu L$. Both products must maintain a pH of \geq 6.2. They are indicated for bleeding due to thrombocytopenia or thrombocytopathy. SDP is preferred for patients alloimmunized to HLA or platelet antigens to limit donor exposure. Both preparations must be stored at $20\,^\circ C$ to $24\,^\circ C$ with continuous agitation and have a shelf-life of $5\,days$.

Plasma Derivatives and Coagulation Factors

Cryoprecipitate is indicated for Fibrinogen deficiency, Hemophilia A, von Willebrand disease, and Factor XIII deficiency. It is stored frozen at $-18\,^\circ C$ or colder. After thawing, it should be kept at room temperature with a shelf-life of $6\,hours$ if unpooled and $4\,hours$ if pooled. Fibrin glue, composed of Cryoprecipitate and topical thrombin, is a commercially prepared, viral-inactivated product used to control bleeding in cardiovascular surgeries.

Plasma Cryoprecipitate Reduced (also known as Cryopoor Plasma or CPP) is primarily used to treat Thrombotic Thrombocytopenic Purpura (TTP) because it contains ADAMTS13. It differs from FFP as it lacks fibrinogen and Factor VIII. It is stored frozen for up to $1\,year$ and can be kept at $1\,^\circ C$ to $6\,^\circ C$ for $5\,days$ after thawing.

Granulocytes collected via apheresis are used for patients with granulocyte dysfunction or myeloid hypoplasia that is unresponsive to antibiotics. These are stored at $20\,^\circ C$ to $24\,^\circ C$ without agitation and must be used within $24\,hours$. Factor VIII and Factor IX concentrates are lyophilized products used to control bleeding in Hemophilia A and Hemophilia B, respectively, and are stored at $1\,^\circ C$ to $6\,^\circ C$. Albumin or Plasma Protein Fraction is used to replace colloids in cases of hypovolemic shock or severe burns and can be stored at $2\,^\circ C$ to $10\,^\circ C$ for $5\,years$.

Irradiation of Blood Components and GVHD Prevention

Blood components containing viable lymphocytes, including RBCs, platelets, and granulocytes, should undergo irradiation to prevent the proliferation of transfused T lymphocytes, which causes Graft-Versus-Host Disease (GVHD). Irradiation is performed using Cesium-137 or Cobalt-60. The recommended dose is a minimum of $25\,Gy$ to the central portion of the container, with no less than $15\,Gy$ delivered to any other part of the bag. Following irradiation, red cells expire after $28\,days$ or at the end of their original storage period, whichever is sooner.

Patients who require irradiated blood include fetuses receiving intrauterine transfusions, hematological transplant recipients, and recipients of HLA-compatible or directed-donor units from blood relatives. This precaution is necessary for both immunocompetent and immunocompromised recipients depending on the clinical context.

Clinical Indications for Blood Components

The selection of blood components is dictated by specific clinical conditions. For active bleeding, whole blood or packed RBCs (pRBCs) are recommended, while massive bleeding may require platelets and FFP. Transient anemia is treated with pRBCs. Aplastic anemia often requires washed or leukoreduced RBCs. Routine surgery utilizes whole blood or pRBCs. Cardiopulmonary bypass procedures use RBCs and crystalloid solutions, and sometimes FFP and platelets.

Repeated febrile reactions call for leukoreduced components, while repeated allergic reactions necessitate washed RBCs or plasma-reduced platelets. Intrauterine transfusions require CMV-negative Group O Rh-negative RBCs, which should be considered for irradiation. Exchange transfusions also require CMV-negative whole blood or packed Group O Rh-negative RBCs. Patients with Anti-IgA antibodies must receive washed RBCs or blood from IgA-deficient donors. Coagulopathies are treated with FFP, and fibrinogen deficiencies are addressed with Cryoprecipitate or FFP. von Willebrand disease is managed with DDAVP or Cryoprecipitate. Shock without hemorrhage is treated with albumin or crystalloids, and cerebral edema may require $25\%$ albumin alongside diuretic therapy.

Classification and Timing of Transfusion Reactions

Transfusion reactions are broadly classified by their timing and pathophysiology. Immediate reactions occur during the transfusion or up to $24\,hours$ afterward, while delayed reactions manifest after $24\,hours$. These are further divided into immunologic and non-immunologic categories. Immediate immunologic reactions include Hemolytic, Febrile, Allergic, and Transfusion-Related Acute Lung Injury (TRALI). Immediate non-immunologic reactions include bacterial contamination and circulatory overload. Delayed immunologic reactions include Hemolytic reactions, Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD), and Post-transfusion purpura. Delayed non-immunologic reactions include TA-hemosiderosis and disease transmission.

Acute Immune Hemolytic Transfusion Reaction (AIHTR)

An Acute Immune Hemolytic Transfusion Reaction (AIHTR) is a severe event where red or dark urine or diffuse oozing may be the only visible signs in an anesthetized patient. Common symptoms include fever, chills, back pain, hypotension, renal failure, and shock, potentially leading to disseminated intravascular coagulation (DIC). Diagnostic markers include a positive Direct Antiglobulin Test (DAT), decreased hemoglobin and haptoglobin, and increased levels of LDH and bilirubin. Treatment requires immediate discontinuation of the transfusion, maintenance of vascular access, blood pressure, and renal blood flow, and management of DIC. Prevention is centered on strict adherence to standard operating procedures for patient identification.

Febrile and Allergic Transfusion Reactions

A Febrile Nonhemolytic Transfusion Reaction (FNHTR) is defined as a temperature increase of $1\,^\circ C$ or more associated with transfusion that is not explained by another condition. Symptoms include fever, chills, nausea, and tachycardia. The DAT is negative in these cases. Treatment includes antipyretics and meperidine for rigors; prevention involves prestorage leukoreduction.

Allergic reactions result from recipient antibodies reacting to transfused donor plasma proteins. Mild allergic reactions present with erythema and pruritus and are treated with antihistamines. Severe allergic reactions—anaphylactic or anaphylactoid—can cause bronchoconstriction, angioedema, hypotension, and cardiac arrest. Anaphylactic reactions can occur after the infusion of only a few milliliters of blood, often due to anti-IgA in the recipient reacting to donor IgA. Treatment for severe reactions involves epinephrine and respiratory support. IgA-deficient patients must receive IgA-deficient blood components, such as washed or frozen RBCs.

Transfusion-Related Acute Lung Injury (TRALI)

TRALI is characterized by noncardiogenic pulmonary edema and is attributed to donor plasma containing high concentrations of leukoagglutinins directed against recipient leukocytes. Symptoms include severe hypoxemia without evidence of left atrial hypertension. Diagnosis is supported by bilateral infiltrates on a chest x-ray and testing for HLA or Human Neutrophil Antigen (HNA) antibodies in the donor. Treatment involves discontinuing the transfusion, supplemental oxygen, and mechanical ventilation. To prevent TRALI, the use of male-only plasma is encouraged, and female platelet donors are often screened or excluded. Donors previously implicated in TRALI should only provide units if they are later processed as deglycerolized or washed RBCs.