Blood Transfusion

Introduction and Immunohematology Principles

• Blood banking and transfusion medicine encompass the procurement, storage, and administration of blood products, immunohematology, and clinical transfusion guidelines tailored specifically to neonatal and pediatric populations.
• Red blood cells (RBCs) express antigens, predominantly the major A, B, and H antigens composed of carbohydrates.
• The H antigen is a precursor to A and B antigens; individuals possessing only the H antigen are categorized as blood group O.
• Naturally occurring antibodies (predominantly IgM subtype) directed against ABO antigens are produced by the humoral immune system around 4 to 6 months of age.
• Blood group O individuals produce naturally occurring anti-A and anti-B isohemagglutinins of the IgM subclass, as well as a unique anti-A,B IgG antibody.
• Because IgG antibodies can cross the placenta, the unique anti-A,B IgG in group O mothers can bind to A or B antigens on infant erythrocytes, precipitating hemolytic disease of the fetus and newborn (HDFN).
• Over 300 minor blood groups exist, with the Rhesus (Rh) system (D antigen) and minor antigens like Kell (K, k), Kidd (Jka, Jkb), and Duffy (Fya, Fyb) being highly immunogenic.
• Exposure to foreign RBC antigens through transfusion or pregnancy can provoke the formation of alloantibodies, which mediate acute or delayed hemolytic transfusion reactions.
• Autoantibodies directed against a recipient's own RBC antigens can form secondary to illness or viral triggers, leading to autoimmune hemolytic anemia.

Blood Collection, Processing, and Storage

• Whole blood (approximately 450-500 mL) is collected and undergoes centrifugation and processing to separate it into RBCs, platelets, and plasma.
• Collected whole blood is mixed with anticoagulant-preservative agents such as acid-citrate-dextrose (ACD), citrate-phosphate-dextrose (CPD), or citrate-phosphate-dextrose-dextrose (CP2D), all of which permit a shelf life of 21 days.
• Citrate-phosphate-dextrose-adenine (CPDA-1) extends the shelf life of whole blood or RBCs to 35 days.
• The incorporation of additive solutions (AS-1, AS-3, AS-5), containing variable concentrations of mannitol, adenine, sodium chloride, and dextrose, further extends the RBC shelf life to 42 days.

Blood Component Modifications

Leukoreduction

• Prestorage filtration of white blood cells (WBCs) from RBCs or platelets ensures that 85% of the original red cell mass remains while reducing the leukocyte count to no more than 5 × 10^6 WBCs per unit.
• Leukoreduction significantly decreases the incidence of febrile nonhemolytic transfusion reactions (FNHTR), transmission of cell-associated viruses such as cytomegalovirus (CMV), and human leukocyte antigen (HLA) alloimmunization.

Irradiation

• Irradiation utilizes X-rays or gamma rays (cesium or cobalt) at a dose of 25 to 50 Gray to cross-link the DNA of T-lymphocytes, rendering them incapable of replication.
• This modification fundamentally prevents transfusion-associated graft-versus-host disease (TA-GVHD).
• Indications for irradiated products include congenital or acquired cellular immunodeficiency, hematopoietic stem cell transplant (HSCT) recipients, premature infants weighing less than 1.2 kg, recipients of intrauterine transfusions, and recipients of directed donations from blood relatives (to prevent engraftment of HLA-homozygous haploidentical lymphocytes).
• Irradiation of RBCs can hasten hemolysis, causing leakage of free hemoglobin and potassium, which carries a risk of dysrhythmia during administration.

Washing and Volume Reduction

• Washing RBCs and platelets removes plasma and anticoagulants, resuspending the cellular component in a solution such as normal saline.
• Washing is indicated to decrease anaphylactic reactions caused by plasma proteins (e.g., in patients with IgA deficiency), to remove excess potassium during large-volume transfusions, or to remove maternal antibodies from platelets used for neonatal alloimmune thrombocytopenia.
• The washing process utilizes an open system, reducing the product's expiration time to 24 hours for RBCs and 4 hours for platelets due to the risk of bacterial contamination.
• Volume reduction involves centrifuging the product and removing the plasma supernatant in a closed system; this concentrates the product without altering the expiration date, which is highly beneficial for neonates at risk of fluid overload.

Blood Products: Characteristics, Indications, and Dosing

Red Blood Cells (RBCs)

• Storage and Volume: Stored at 4°C for up to 42 days (depending on the additive solution); standard unit volume is approximately 300 mL.
• Indications: Acute blood loss, chronic symptomatic anemia, decreased RBC production due to acquired (chemotherapy) or congenital (bone marrow failure) causes, and for optimizing tissue oxygenation.
• Dose and Administration: The standard pediatric dose is 10 to 15 mL/kg (maximum 1 unit), infused slowly over 2 to 4 hours with careful monitoring to prevent transfusion-associated circulatory overload (TACO).
• Sterile Docking: A single RBC unit can be redistributed into multiple aliquots within a closed system, maintaining the original expiration date and allowing repeated transfusions for a single infant from the same donor to minimize alloimmunization and infectious exposures.

Platelets

• Storage and Volume: Stored at 20°C to 24°C with continuous agitation for 5 to 7 days; apheresis unit volume is roughly 300 mL, while a whole-blood derived platelet concentrate is about 50 mL.
• Dose and Administration: The standard pediatric dose is 10 to 15 mL/kg, or 4 to 6 pooled platelet concentrates, or 1 apheresis unit for larger children; infused rapidly over 1 to 4 hours.
• Indications: Transfused for severe thrombocytopenia with bleeding, or prophylactically prior to invasive procedures.
• Platelet Refractoriness: Defined by poor response measured via a 1-hour post-transfusion count; it requires investigation for immune (HLA/HPA alloantibodies) or nonimmune causes, and may necessitate HLA-matched or cross-matched single-donor platelets.

Plasma

• Storage and Volume: Fresh frozen plasma (FFP) or plasma frozen within 24 hours (F24) is stored at -18°C or colder for up to 12 months; standard unit volume is roughly 200 mL.
• Dose and Administration: The standard pediatric dose is 15 mL/kg (maximum 1 unit), infused over 2 hours.
• Compatibility: Plasma must be strictly ABO-compatible with the recipient's RBCs to prevent minor crossmatch incompatibility, where donor isohemagglutinins destroy recipient erythrocytes.
• Indications: Deficiencies of multiple coagulation factors (e.g., liver failure, severe disseminated intravascular coagulation with bleeding), emergency reversal of warfarin, dilutional coagulopathy in massive transfusion, and as replacement fluid during therapeutic plasma exchange for thrombotic thrombocytopenic purpura (TTP).
• Contraindications: Plasma is not indicated for the simple correction of hypovolemia or as an immunoglobulin replacement therapy.

Cryoprecipitate

• Storage and Volume: Stored at -18°C or colder for up to 12 months; unit volume is very small, approximately 20 mL.
• Composition: Contains highly concentrated fibrinogen, fibronectin, von Willebrand factor, factor VIII, and factor XIII.
• Dose and Administration: The typical dose is 1 to 2 units per 5 to 10 kg of body weight, which can rapidly raise plasma fibrinogen levels by 60 to 100 mg/dL.
• Indications: Primarily utilized to treat acquired or congenital hypofibrinogenemia.

Granulocytes

• Storage and Volume: Stored at 4°C with a maximum shelf life of 24 hours; product volume is variable.
• Preparation: Donors undergo stimulation with oral corticosteroids and granulocyte colony-stimulating factor (G-CSF) 12 to 18 hours prior to leukapheresis to increase collection yield.
• Compatibility: The product cannot be leukoreduced, contains significant RBC contamination, and strictly requires irradiation and ABO crossmatching prior to administration.
• Dose and Administration: Neonates and infants weighing less than 10 kg receive 1 to 2 × 10^9 neutrophils/kg; larger children require a minimum total dose of 1 × 10^10 neutrophils per transfusion, administered daily until infection resolves or absolute neutrophil count recovers.
• Indications: Severe, prolonged neutropenia (blood neutrophil count <0.5 × 10^9/L) associated with progressive bacterial, yeast, or fungal infection unresponsive to appropriate antimicrobial therapy, or in patients with qualitative neutrophil dysfunction syndromes.

Pediatric and Neonatal Transfusion Guidelines

Children and Adolescents

• RBC Transfusion Triggers: Transfusion is indicated to maintain hemodynamic stability following an acute loss of >25% of circulating blood volume.
• In the perioperative period, maintaining a hemoglobin level >7.0 g/dL is generally acceptable for most stable pediatric patients.
• For children with severe cardiopulmonary disease or those managed on extracorporeal membrane oxygenation (ECMO), restrictive thresholds are abandoned, and hemoglobin is maintained >12.0 g/dL.
• Platelet Transfusion Triggers: Maintain platelet count >50 × 10^9/L during active bleeding or for major invasive procedures.
• For minor invasive procedures, maintaining a platelet count >25 × 10^9/L is acceptable.
• In patients with bone marrow failure, maintain platelet count >20 × 10^9/L if hemorrhagic risk factors (e.g., fever, sepsis, mucosal lesions) are present, but a lower threshold of >10 × 10^9/L is utilized for stable patients without bleeding risks.

Neonates and Preterm Infants

• Physiologic Anemia vs. Anemia of Prematurity: Healthy term infants experience a benign, physiologic decline in hemoglobin to a nadir of roughly 11 g/dL at 8-12 weeks, which requires no transfusion. Preterm infants suffer a more extreme decline (anemia of prematurity) reaching 7-9 g/dL by 3-6 weeks, exacerbated by shortened RBC lifespan, rapid growth, blunted erythropoietin response, and iatrogenic phlebotomy losses.
• Neonatal RBC Guidelines: Maintain hemoglobin >12.0 g/dL for severe pulmonary or cardiac disease and during ECMO. Maintain hemoglobin >10.0 g/dL preoperatively, during major surgery, or with moderate pulmonary disease.
• The routine practice of transfusing exclusively "fresh" RBCs (<7 days storage) to neonates is unsupported by clinical trials; RBCs stored up to 42 days via dedicated single-donor aliquots are standard of care and do not increase the risk of necrotizing enterocolitis or intraventricular hemorrhage.
• CMV Prevention: To prevent transfusion-transmitted CMV (TT-CMV) in low birthweight infants (<1500 g), the use of leukocyte-reduced RBCs is mandatory. Some protocols recommend combined leukoreduction and CMV-seronegative units, but transfusion should never be delayed if CMV-negative units are unavailable.
• Neonatal Platelet Guidelines: Prophylactic platelet transfusions to maintain normal platelet counts are not beneficial. Maintain platelets >50 × 10^9/L for invasive procedures, active bleeding, or clinical instability; maintain >20 × 10^9/L if the infant is clinically stable.

Transfusion in Hemoglobinopathies

• Thalassemia Major: Chronic, regular RBC transfusions are initiated for hemoglobin <7 g/dL or when accompanied by poor growth, facial bone deformities, or extramedullary hematopoiesis.
• The goal of chronic transfusion in beta-thalassemia is to maintain a pre-transfusion hemoglobin level of 9.5 to 10.5 g/dL to suppress endogenous ineffective erythropoiesis.
• Sickle Cell Disease (SCD): Short-term episodic transfusions are indicated for acute chest syndrome, aplastic crisis, splenic sequestration, prior to high-risk surgery, or acute stroke.
• For acute stroke, immediate simple blood transfusion targetting a maximum hemoglobin of 10 g/dL is performed to prevent hyperviscosity, rapidly followed by exchange transfusion (erythrocytapheresis) to reduce the HbS fraction to <30%.
• Chronic transfusion protocols (maintaining HbS <30%) are mandatory for primary and secondary stroke prophylaxis in SCD patients with abnormal transcranial Doppler ultrasound velocities or prior stroke history.
• Alloimmunization Prevention: Patients with SCD have an exceptionally high alloimmunization risk (17.6%), most commonly forming antibodies against Rh (C, E) and Kell antigens. All chronically transfused hemoglobinopathy patients must receive leukoreduced blood that is extended antigen-matched for D, C, c, E, e, and Kell.
• Iron Overload: Chronic transfusions inevitably cause hemosiderosis, defined by serum ferritin >1000 ng/mL or liver iron concentration >5 mg/g dry weight, mandating accurate quantification via MRI T2* imaging of the liver and heart.
• Management necessitates rigorous daily iron chelation using subcutaneous deferoxamine, oral deferasirox, or oral deferiprone to avert fatal endocrine and cardiac toxicities.

Massive Transfusion Protocols (MTP)

• Massive transfusion in pediatrics is defined as the administration of >40 mL/kg total of all blood products, or the replacement of one entire estimated blood volume (roughly 60 mL/kg) within a short timeframe.
• MTPs aim for the rapid, balanced administration of RBCs, plasma, and platelets at a targeted 1:1:1 ratio to mimic whole blood.
• The primary objective is to simultaneously restore oxygen-carrying capacity, expand circulating blood volume, and correct trauma-induced or dilutional coagulopathy, acidosis, and hypothermia.
• Viscoelastic testing (e.g., thromboelastography) is increasingly utilized to guide goal-directed hemostatic resuscitation, minimizing inappropriate plasma or platelet usage.

Transfusion Reactions and Complications

• Acute Hemolytic Transfusion Reaction (AHTR): A severe, immediate (0-24 hours) complication primarily driven by ABO incompatibility (e.g., group A blood given to a group O recipient). It causes rapid intravascular hemolysis presenting with fever, chills, rigors, flank pain, hemoglobinuria, hypotension, and a feeling of impending doom.
• Delayed Hemolytic Transfusion Reaction (DHTR): Occurs days to weeks (typically 24 hours to 10 days) post-transfusion, resulting from an anamnestic antibody response to minor RBC antigens. It features extravascular hemolysis presenting as pallor, jaundice, and dropping hemoglobin, which frequently mimics a vaso-occlusive pain crisis in patients with SCD.
• Febrile Nonhemolytic Transfusion Reaction (FNHTR): Characterized by an incremental temperature increase of ≥1°C above baseline without other specific symptoms. It is mediated by donor proinflammatory cytokines or recipient antibodies against donor leukocytes, and its incidence is drastically reduced by prestorage leukoreduction.
• Allergic and Anaphylactic Reactions: IgE-mediated type I hypersensitivity reactions against plasma proteins. Symptoms range from mild urticaria (hives/rash) to severe anaphylaxis (bronchospasm, hypotension). Management requires temporary cessation of the transfusion, antihistamines, or intramuscular epinephrine and washed RBCs for severe recurring cases.
• Transfusion-Related Acute Lung Injury (TRALI): An acute respiratory complication (0-6 hours post-transfusion) caused by donor antibodies reacting with recipient HLA or human neutrophil antigens (HNA). It manifests as acute noncardiogenic pulmonary edema, hypoxia, and bilateral interstitial infiltrates on chest radiograph.
• Transfusion-Associated Circulatory Overload (TACO): Volume overload resulting in cardiogenic pulmonary edema, characterized by dyspnea, orthopnea, jugular venous distention, tachycardia, hypertension, widened pulse pressure, and elevated brain natriuretic peptide. Management requires diuretics, oxygen, and slower subsequent transfusion rates.
• Septic Transfusion Reactions: Arise from bacterial contamination of blood products, disproportionately affecting platelets due to their mandatory room temperature storage. Symptoms include fever with rigors, emesis, and hypotensive shock.
• Transfusion-Transmitted Infections (TTI): Rigorous donor screening and nucleic acid testing have dramatically reduced viral transmission. The estimated residual risk in the United States is 1 in 2 million for HIV and HCV, and 1 in 1.7 million for HBV. Other rare pathogens include syphilis, parvovirus B19, West Nile virus, Babesia, and Zika virus.
• Management of Suspected Reactions: Immediately halt the transfusion, maintain venous access with normal saline, assess patient airway and hemodynamics, verify unit and patient identification, notify the blood bank, and send the implicated unit alongside post-transfusion blood and urine samples for laboratory investigation.

Patient Blood Management

• Patient Blood Management (PBM) is a multidisciplinary, evidence-based approach designed to optimize the care of patients who might need transfusions, thereby minimizing unnecessary blood product utilization.
• Core tenets of PBM include the timely preoperative diagnosis and correction of anemia (e.g., using recombinant human erythropoietin and intravenous iron).
• Surgical strategies involve employing minimally invasive (laparoscopic) techniques, using intraoperative cell salvage systems, and administering antifibrinolytic agents (aminocaproic acid or tranexamic acid) to control surgical or mucosal bleeding.
• These strategies collectively improve patient survival, reduce the average length of hospital stay, minimize exposure to alloantigens and transfusion reactions, and generate substantial healthcare cost savings.