# Transfusion Medicine - Components and Reactions

## Introduction

Transfusion medicine encompasses the collection, processing, testing, storage, and clinical application of blood components, representing a discipline that intersects hematology, immunology, and patient safety science. Approximately 16 million units of blood components are transfused annually in the United States, each carrying both therapeutic potential and real risks. The decision to transfuse should never be reflexive; rather, each transfusion must be evaluated as a clinical intervention in which the potential benefit is weighed against the risk of adverse events including hemolytic reactions, transfusion-related lung injury, circulatory overload, infectious transmission, and immunologic sensitization. Patient blood management (PBM) strategies, which aim to optimize the patient's own hemoglobin, minimize blood loss, and harness the patient's physiologic tolerance of anemia, have emerged as a comprehensive framework for reducing unnecessary transfusions and improving patient outcomes.

## Blood Components

### Packed Red Blood Cells (PRBCs)

Packed red blood cells are prepared by centrifugation of whole blood with removal of the majority of plasma, yielding a product with a volume of approximately 300 mL and a hematocrit of 55 to 65%. Storage occurs at 1 to 6 degrees Celsius using additive solutions such as CPDA-1, AS-1, AS-3, or AS-5, which extend the shelf life to a maximum of 42 days. During storage, red blood cells undergo the "storage lesion," a progressive series of biochemical and structural changes that include depletion of 2,3-diphosphoglycerate (2,3-DPG) and ATP, potassium leakage from the intracellular compartment into the supernatant, and generation of procoagulant and proinflammatory microparticles. The clinical significance of the storage lesion has been extensively debated, but large randomized trials have demonstrated no clear benefit of fresh over standard-issue red blood cells for most patient populations. Importantly, 2,3-DPG levels regenerate within 24 hours of transfusion, restoring normal oxygen dissociation kinetics. The expected hemoglobin rise from a single unit of PRBCs is approximately 1 g/dL in a 70 kg adult who is not actively bleeding.

Transfusion thresholds have been refined through multiple landmark randomized controlled trials. The restrictive threshold of hemoglobin 7 g/dL or below is appropriate for the majority of hemodynamically stable, non-bleeding hospitalized patients, supported by the TRICC trial in critical care, the TITRe2 trial in cardiac surgery, the TRACS trial in cardiac surgery, and the FOCUS trial in hip fracture patients. A liberal threshold of hemoglobin 8 g/dL or below may be considered for patients with acute coronary syndromes or symptomatic cardiovascular disease. Higher thresholds are appropriate for patients with active hemorrhage, hemodynamic instability, or symptoms directly attributable to anemia. In sickle cell disease, the target hemoglobin for simple transfusion is 10 g/dL, and levels should not exceed 10 g/dL to prevent hyperviscosity, which can paradoxically precipitate vaso-occlusive complications.

| Component | Volume | Storage | Shelf Life | Expected Effect per Unit | Key Contents |
|-----------|--------|---------|------------|-------------------------|-------------|
| PRBCs | ~300 mL | 1–6°C | 42 days (with additive) | ↑ Hb ~1 g/dL | RBCs (Hct 55–65%) |
| Platelets (apheresis) | ~250 mL | 20–24°C with agitation | 5 days | ↑ Plt 20,000–40,000/μL | ~3 × 10¹¹ platelets |
| FFP | ~250 mL | Frozen; thaw 30–45 min | 1 year frozen; 5 days thawed | ↑ Factors ~30% (at 10–15 mL/kg) | All coagulation factors, fibrinogen 2–4 mg/mL |
| Cryoprecipitate | ~15 mL/unit | Frozen | 1 year frozen | ↑ Fibrinogen 5–10 mg/dL per unit | Fibrinogen (~250 mg), FVIII (~80 IU), FXIII, VWF |

| Transfusion Threshold | Clinical Context |
|----------------------|-----------------|
| Hb ≤7 g/dL | Most hemodynamically stable, non-bleeding hospitalized patients (TRICC, FOCUS, TITRe2, TRACS) |
| Hb ≤8 g/dL | Acute coronary syndrome, symptomatic cardiovascular disease |
| Plt <10,000 | Prophylactic threshold — stable, non-bleeding patients |
| Plt <20,000 | Fever, sepsis, or DIC |
| Plt <50,000 | Invasive procedures; active bleeding |
| Plt <100,000 | Neurosurgery or ocular surgery |
| Fibrinogen <150 mg/dL | DIC |
| Fibrinogen <200 mg/dL | Massive hemorrhage |

Several modifications of PRBCs are available to address specific clinical needs. Leukoreduction, which removes greater than 99.9% of white blood cells through filtration, is now standard practice at most blood centers in the United States and substantially reduces febrile non-hemolytic transfusion reactions, CMV transmission, and HLA alloimmunization. Irradiation with 25 to 50 Gray of gamma radiation prevents transfusion-associated graft-versus-host disease (TA-GVHD) by inactivating residual donor T lymphocytes. Irradiated products are mandatory for immunocompromised patients (including HSCT recipients, patients receiving purine analogue chemotherapy such as fludarabine or cladribine, and those with congenital immunodeficiency), for HLA-matched or directed donations (which increase the risk of TA-GVHD due to shared HLA haplotypes), and for intrauterine transfusions. CMV-negative products, sourced from donors who test negative for CMV antibodies, are indicated for CMV-seronegative transplant recipients, though leukoreduction is widely considered to provide a "CMV-safe" equivalent. Washed products, from which residual plasma has been removed through saline washing, are indicated for patients with IgA deficiency who have developed anti-IgA antibodies (which carry a risk of anaphylaxis) and for patients with severe or recurrent allergic transfusion reactions. Extended phenotype matching, involving Rh antigens (C, c, E, e) and Kell, is standard practice for chronically transfused patients with sickle cell disease and thalassemia to minimize the risk of alloimmunization.

### Platelets

Platelets are available as either apheresis platelets (collected from a single donor, providing approximately 3 x 10^11 platelets per unit) or pooled whole-blood-derived platelets (in which 4 to 6 random donor units are combined). Storage occurs at room temperature (20 to 24 degrees Celsius) with continuous gentle agitation to maintain viability and prevent aggregation. The shelf life is limited to 5 days, primarily due to the increasing risk of bacterial contamination with extended room-temperature storage.

Bacterial contamination is the most common infectious risk associated with transfusion, and platelets are the component most frequently implicated due to their room-temperature storage. Both gram-positive organisms (Staphylococcus and Streptococcus species) and gram-negative organisms can contaminate platelet products. Pathogen reduction technology (PRT), such as the Intercept system using amotosalen and ultraviolet A light, inactivates bacteria, viruses, and parasites in platelet products and has been increasingly adopted to mitigate this risk.

The expected platelet count increment from one apheresis unit is 20,000 to 40,000 per microliter in a 70 kg adult. Transfusion thresholds are stratified by clinical context: a prophylactic threshold of 10,000 is used for stable patients without bleeding; 20,000 is appropriate for patients with fever, sepsis, or DIC; 50,000 is targeted before invasive procedures; and 100,000 is required for neurosurgery or ocular surgery. For patients with active bleeding, the goal is to maintain a count above 50,000, with a higher target of 100,000 for hemorrhage in critical anatomic locations.

Platelet refractoriness, defined as the failure to achieve the expected post-transfusion increment, is a common clinical problem. Non-immune causes are far more prevalent and include fever, sepsis, DIC, splenomegaly, and medications. Immune-mediated refractoriness results from HLA alloimmunization in multiply-transfused patients and is formally diagnosed when the corrected count increment (CCI) is below 5,000 at 10 to 60 minutes on two consecutive transfusions. Management of immune-mediated refractoriness requires either HLA-matched platelets selected from the donor registry or crossmatch-compatible platelets.

### Fresh Frozen Plasma (FFP)

Fresh frozen plasma is prepared by separating and freezing plasma within 8 hours of whole blood collection, preserving all coagulation factors, fibrinogen (at a concentration of 2 to 4 mg/mL), and the natural anticoagulant proteins. Each unit has a volume of approximately 250 mL and must be ABO-compatible with the recipient. Thawing requires 30 to 45 minutes, a logistical consideration in emergencies. Once thawed, plasma can be stored at 1 to 6 degrees Celsius for up to 5 days, though some loss of labile factors V and VIII occurs during extended storage.

The standard dose of FFP is 10 to 15 mL/kg, which provides an approximately 30% increase in coagulation factor levels. Appropriate indications include active bleeding with documented coagulopathy (PT or aPTT greater than 1.5 times the control), massive transfusion protocols, therapeutic plasma exchange for thrombotic thrombocytopenic purpura (as the replacement fluid), and warfarin reversal when PCC is unavailable. FFP is explicitly not indicated for volume resuscitation, nutritional supplementation, or the "correction" of mildly elevated INR values in non-bleeding patients, as these represent common patterns of inappropriate utilization.

### Cryoprecipitate

Cryoprecipitate is the cold-insoluble precipitate obtained by slowly thawing fresh frozen plasma at 1 to 6 degrees Celsius. Each unit, approximately 15 mL in volume, contains concentrated quantities of fibrinogen (approximately 250 mg per unit), factor VIII (approximately 80 IU per unit), factor XIII, von Willebrand factor, and fibronectin. Units are typically pooled in bags of 5 to 10 for clinical use.

The standard dose is 1 unit per 5 kg of body weight, typically amounting to 10 units (one pool) for a 70 kg adult. Each unit is expected to raise the fibrinogen level by approximately 5 to 10 mg/dL. The primary indication for cryoprecipitate is hypofibrinogenemia, with a target of above 150 mg/dL in DIC and above 200 mg/dL in massive hemorrhage. Additional uses include treatment of factor XIII deficiency, adjunctive treatment of uremic bleeding (utilizing its VWF content), and preparation of fibrin sealant.

Fibrinogen concentrate (RiaSTAP) is a purified, pathogen-reduced alternative that offers several practical advantages: it does not require thawing, can be reconstituted rapidly, provides a standardized dose, and eliminates the residual infectious risk associated with pooled cryoprecipitate. A dose of 70 mg/kg raises fibrinogen levels by approximately 100 mg/dL. Fibrinogen concentrate is increasingly preferred over cryoprecipitate in many clinical settings.

<image>A blood component reference diagram showing four panels, one for each major blood component (PRBCs, platelets, FFP, cryoprecipitate). For each panel, display: a visual representation of the component bag with color coding (red for PRBCs, yellow/golden for platelets, light yellow for FFP, small aliquot for cryo), storage conditions (temperature, duration, special requirements like agitation for platelets), key contents (Hb, WBCs for PRBCs; platelet count for platelets; all factors for FFP; fibrinogen, FVIII, VWF for cryo), expected clinical effect per unit, transfusion thresholds, ABO compatibility requirements, and common modifications (leukoreduced, irradiated, washed, pathogen-reduced). Include a quick-reference dosing table at the bottom. Medical laboratory reference card style with clean, organized layout.</image>

## Transfusion Reactions

### Acute Hemolytic Transfusion Reaction (AHTR)

Acute hemolytic transfusion reactions represent the most feared and potentially fatal complication of transfusion. The vast majority are caused by ABO-incompatible transfusion resulting from clerical errors in patient identification, specimen labeling, or unit selection rather than from laboratory testing failures. When ABO-incompatible red blood cells encounter preformed IgM antibodies in the recipient's plasma, complement activation proceeds through the classical pathway to completion, resulting in intravascular hemolysis with release of free hemoglobin, activation of the coagulation cascade, and cytokine-mediated systemic inflammation.

Symptoms typically manifest within minutes of initiating the transfusion and include fever, chills, flank pain, chest pain or tightness, dyspnea, hypotension, tachycardia, and hemoglobinuria (dark or red urine). The reaction may progress to DIC, acute renal failure from hemoglobin-mediated tubular injury, and cardiovascular collapse. In anesthetized patients, hypotension and diffuse microvascular bleeding may be the only signs. Management requires immediate cessation of the transfusion, aggressive intravenous fluid resuscitation to maintain urine output above 1 mL/kg/hr to prevent renal tubular necrosis, and a transfusion reaction workup that includes a direct antiglobulin test (DAT), repeat type and screen on a freshly drawn specimen, and visual inspection of the post-transfusion plasma for hemolysis (pink or red discoloration indicating free hemoglobin). Monitoring for DIC and renal failure is essential. Prevention depends entirely on rigorous patient and specimen identification at the bedside, typically enforced through two-person verification protocols at the time of both specimen collection and transfusion administration.

### Delayed Hemolytic Transfusion Reaction (DHTR)

Delayed hemolytic transfusion reactions occur 2 to 14 days after transfusion and result from an anamnestic immune response to minor red blood cell antigens, most commonly those of the Kidd, Duffy, Kell, and Rh systems. At the time of the initial crossmatch, the patient's antibody levels were below the threshold of detection, allowing apparently compatible units to be issued. Upon re-exposure to the antigen, a secondary immune response produces IgG antibodies that mediate extravascular hemolysis through splenic sequestration and destruction of the transfused antigen-positive red cells.

The clinical presentation is typically milder than AHTR, manifesting as an unexplained decline in hemoglobin below the expected post-transfusion level, low-grade fever, mild jaundice with an elevated indirect bilirubin, and a newly positive DAT. The newly identified antibody is documented in the patient's transfusion record to guide future transfusions. Most DHTRs are self-limited, though Kidd antibodies deserve particular caution as they can cause brisk and clinically significant hemolysis.

A particularly dangerous variant of DHTR occurs in patients with sickle cell disease: hyperhemolysis syndrome. In this condition, the immune-mediated destruction of transfused red blood cells triggers the concurrent destruction of the patient's own autologous red blood cells through a mechanism that is not fully understood but may involve bystander hemolysis and reticulocyte suppression. The hallmark is a hemoglobin level that drops below the pre-transfusion baseline, accompanied by reticulocytopenia, a finding that distinguishes hyperhemolysis from simple DHTR. Critically, further transfusion in this setting may paradoxically worsen the anemia and can be fatal. Management includes avoidance of additional transfusions, IVIG, corticosteroids, and in refractory cases, eculizumab or rituximab.

### Febrile Non-Hemolytic Transfusion Reaction (FNHTR)

Febrile non-hemolytic transfusion reactions are the most common transfusion reaction overall, occurring in approximately 1% of transfusions. They are caused by cytokines that accumulate in stored blood products from residual white blood cells or by recipient antibodies directed against donor leukocyte antigens. The clinical presentation consists of fever (defined as a rise of 1 degree Celsius or more above baseline), chills, and rigors without evidence of hemolysis. The primary management concern is to stop the transfusion and rule out more serious causes of fever during transfusion, specifically hemolytic reactions and bacterial contamination, before attributing the reaction to FNHTR. Once these diagnoses are excluded, acetaminophen provides symptomatic relief, and the transfusion may be resumed if clinically appropriate. Leukoreduction has significantly reduced the incidence of FNHTR.

### Allergic Reactions

Mild allergic transfusion reactions, consisting of urticaria, pruritus, and flushing, occur in 1 to 3% of transfusions and are attributed to recipient sensitivity to plasma proteins in the transfused product. Management involves temporarily holding the transfusion, administering diphenhydramine 25 to 50 mg intravenously, and resuming the transfusion once symptoms have resolved.

Anaphylactic reactions are rare (occurring in fewer than 1 in 20,000 transfusions) but life-threatening, presenting with hypotension, bronchospasm, and angioedema. The classic association is with IgA-deficient patients (prevalence approximately 1 in 500 in the general population) who have developed anti-IgA antibodies. Upon exposure to IgA in transfused plasma, a fulminant anaphylactic response ensues. Management follows standard anaphylaxis protocols with immediate epinephrine 0.3 to 0.5 mg intramuscularly, cessation of the transfusion, and aggressive hemodynamic support. Prevention requires washed cellular products to remove residual plasma or, when available, components obtained from IgA-deficient donors.

### Transfusion-Related Acute Lung Injury (TRALI)

Transfusion-related acute lung injury is defined as the acute onset of hypoxemia (PaO2/FiO2 ratio of 300 or less) with bilateral pulmonary infiltrates on chest radiography occurring during or within 6 hours of transfusion, in the absence of evidence of circulatory overload and without pre-existing acute lung injury. The pathogenesis involves donor anti-HLA or anti-HNA (human neutrophil antigen) antibodies present in plasma-containing blood products that bind to recipient neutrophils in the pulmonary vasculature, triggering neutrophil activation, endothelial damage, and capillary leak. The "two-hit" model proposes that a predisposing first hit (such as sepsis, recent surgery, or massive transfusion) primes pulmonary neutrophils, and the transfusion provides the second hit that precipitates the full syndrome.

Management is supportive, consisting of supplemental oxygen and mechanical ventilation when needed. Diuretics are not helpful and may be harmful, as the pulmonary edema is non-cardiogenic and results from capillary permeability rather than hydrostatic pressure. The prognosis is generally favorable, with resolution typically occurring within 48 to 72 hours. TRALI has historically been the leading cause of transfusion-related mortality, but its incidence has decreased substantially following the implementation of male-only plasma policies, which exclude from the plasma donor pool female donors with HLA antibodies acquired through pregnancy.

### Transfusion-Associated Circulatory Overload (TACO)

Transfusion-associated circulatory overload is a form of hydrostatic (cardiogenic) pulmonary edema resulting from the volume load imposed by transfusion. It is now recognized as more common than TRALI, particularly in elderly patients and those with heart failure, renal failure, or fluid overload from other causes. Risk is increased by rapid transfusion rates and the administration of multiple units.

The distinction between TRALI and TACO is clinically important because their management differs fundamentally. Key differentiating features include the BNP level (elevated in TACO, normal in TRALI), the response to diuretics (improvement in TACO, no benefit in TRALI), and the fluid balance (positive in TACO). Prevention of TACO involves slow transfusion rates (1 mL/kg/hr in high-risk patients), administration of diuretics between units, and use of volume-reduced blood products when available.

### Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD)

Transfusion-associated GVHD is a rare but nearly universally fatal complication in which viable donor T lymphocytes within the transfused cellular product engraft in the immunocompromised recipient and mount an immune attack against recipient tissues. Mortality exceeds 90%, far higher than transplant-associated GVHD, primarily because the donor lymphocytes also attack the recipient's bone marrow, producing irreversible pancytopenia. The clinical presentation begins 1 to 2 weeks after transfusion with fever, a characteristic maculopapular rash, diarrhea, hepatitis, and progressive pancytopenia.

At-risk populations include profoundly immunocompromised patients (HSCT recipients, patients on purine analogue therapy, congenital immunodeficiency), recipients of HLA-similar directed donations (particularly from biological relatives, where shared HLA haplotypes allow donor T cells to evade immune surveillance), and fetuses receiving intrauterine transfusions. Prevention requires gamma irradiation (25 to 50 Gy) of all cellular blood products for at-risk patients. It is critical to understand that leukoreduction alone does not prevent TA-GVHD, as the number of T cells remaining after leukoreduction, while substantially reduced, is still sufficient to cause engraftment in susceptible hosts.

| Reaction | Timing | Mechanism | Key Features | Management | Prevention |
|----------|--------|-----------|-------------|------------|------------|
| Acute Hemolytic (AHTR) | Minutes | ABO incompatibility → complement-mediated intravascular hemolysis | Fever, flank pain, hypotension, hemoglobinuria, DIC | Stop transfusion; IV fluids (UOP >1 mL/kg/hr); monitor for DIC/renal failure | Two-person bedside verification |
| Delayed Hemolytic (DHTR) | 2–14 days | Anamnestic IgG response to minor antigens (Kidd, Duffy, Kell, Rh) | Unexpected Hb drop, low-grade fever, jaundice, positive DAT | Usually self-limited; document antibody for future | Extended antigen matching for chronically transfused |
| Febrile Non-Hemolytic (FNHTR) | During/shortly after | Cytokines from residual WBCs; anti-leukocyte antibodies | Fever (≥1°C rise), chills, rigors; no hemolysis | Stop transfusion; rule out hemolysis/sepsis; acetaminophen | Leukoreduction |
| Allergic (mild) | During | Sensitivity to donor plasma proteins | Urticaria, pruritus, flushing | Hold transfusion; diphenhydramine; resume when resolved | Premedication for recurrent reactions |
| Anaphylaxis | Minutes | Anti-IgA antibodies in IgA-deficient recipient | Hypotension, bronchospasm, angioedema | Epinephrine 0.3–0.5 mg IM; stop transfusion | Washed products or IgA-deficient donors |
| TRALI | Within 6 hrs | Donor anti-HLA/HNA antibodies → neutrophil activation in lungs | Hypoxemia (P/F ≤300), bilateral infiltrates, non-cardiogenic edema | Supportive (O₂, ventilation); diuretics NOT helpful | Male-only plasma policy |
| TACO | During/shortly after | Volume overload → hydrostatic pulmonary edema | Dyspnea, hypertension, elevated BNP, positive fluid balance | Diuretics; slow/stop transfusion | Slow rate (1 mL/kg/hr in high-risk); diuretics between units |
| TA-GVHD | 1–2 weeks | Donor T cells engraft → attack recipient tissues including marrow | Rash, diarrhea, hepatitis, pancytopenia; >90% fatal | No effective treatment once established | Irradiation (25–50 Gy) of cellular products for at-risk patients |

### Bacterial Contamination

Bacterial contamination poses the highest infectious risk per unit transfused among all transfusion-related infections. The risk is greatest with platelets due to their room-temperature storage, with an estimated incidence of approximately 1 in 3,000 for pooled platelets. Common organisms contaminating platelets include Staphylococcus and Streptococcus species (gram-positive, reflecting skin flora introduction during collection), while PRBCs are occasionally contaminated with organisms that proliferate at refrigerator temperatures, notably Yersinia enterocolitica and Pseudomonas species. Clinical presentation during transfusion includes high fever, rigors, and hypotension. Management requires immediate cessation of the transfusion, blood cultures from both the patient and the implicated product, and initiation of broad-spectrum antibiotics. Prevention strategies include improved skin antisepsis at the time of collection, diversion of the initial volume of collected blood, bacterial detection testing of platelet products, and increasingly, pathogen reduction technology.

## Massive Transfusion

### Definition and Protocol

Massive transfusion is variably defined as the transfusion of 10 or more units of PRBCs within 24 hours, the transfusion of 4 or more units within 1 hour with an anticipated ongoing need, or the replacement of the patient's entire estimated blood volume. The activation of a massive transfusion protocol (MTP) provides a structured, institutional framework for the rapid delivery of blood products in a balanced ratio.

The optimal component ratio for massive transfusion was addressed by the PROPPR trial, which compared a 1:1:1 ratio of PRBCs to FFP to platelets against a 1:1:2 ratio. The balanced 1:1:1 ratio demonstrated a trend toward improved hemostasis and reduced 24-hour mortality without an increase in complications, and has become the accepted standard for most massive transfusion protocols. Tranexamic acid at 1 g intravenously administered within 3 hours of injury is an essential adjunct based on the CRASH-2 trial, which demonstrated a statistically significant 1.5% reduction in all-cause mortality in trauma patients with significant hemorrhage.

Ongoing laboratory monitoring during massive transfusion is essential. Fibrinogen should be maintained above 150 to 200 mg/dL, as it is the first coagulation factor to reach critically low levels during massive hemorrhage. Ionized calcium must be monitored closely because the citrate anticoagulant present in blood products chelates calcium, and citrate toxicity from massive transfusion produces clinically significant hypocalcemia that impairs both cardiac contractility and coagulation function. Temperature should be maintained above 35 degrees Celsius, and potassium should be monitored as stored red blood cells release potassium into the supernatant. Viscoelastic testing with TEG or ROTEM, when available, provides point-of-care, real-time assessment of clot formation, strength, and fibrinolysis, enabling targeted component therapy that reduces overall transfusion volumes compared to empiric replacement.

The "lethal triad" of hypothermia, acidosis, and coagulopathy represents a self-reinforcing pathophysiologic cycle that, once established, carries extremely high mortality in massive hemorrhage. Each element exacerbates the others: hypothermia impairs coagulation enzyme function, acidosis impairs platelet function and accelerates fibrinolysis, and coagulopathy worsens hemorrhage leading to further hypothermia and acidosis. Active prevention through warming devices, balanced resuscitation, and damage-control surgical strategies is essential.

<image>A massive transfusion protocol (MTP) infographic. At the top, show the activation criteria (clinical indicators: uncontrolled hemorrhage, anticipated need for >10 units PRBCs, hemodynamic instability despite resuscitation). Below, display the balanced resuscitation strategy: cooler packs delivered in 1:1:1 ratio (6 units PRBCs: 6 units FFP: 1 apheresis platelet). Show the laboratory monitoring panel during MTP: CBC, PT/INR, aPTT, fibrinogen, ionized calcium, TEG/ROTEM if available. Include target values: fibrinogen >150-200 mg/dL, platelets >50K, INR <1.5, ionized calcium >1.1 mmol/L, temperature >35C. Display the adjuncts: TXA 1g IV bolus (within 3 hours), calcium gluconate/chloride for citrate toxicity, warming devices. Show the complications to monitor: hypothermia, coagulopathy, acidosis ("lethal triad" with a triangle diagram), hypocalcemia, hyperkalemia. Emergency medicine/trauma style infographic with bold colors and clear layout.</image>

## Key Clinical Pearls

- Restrictive transfusion thresholds (Hb ≤7 g/dL) are appropriate for most hospitalized patients and are supported by multiple RCTs; liberal transfusion does NOT improve outcomes and increases costs/complications
- TRALI is the leading cause of transfusion-related mortality; male-only plasma policies have significantly reduced incidence
- TA-GVHD is nearly 100% fatal; irradiation of cellular products for at-risk patients is non-negotiable
- Hyperhemolysis syndrome in SCD is a life-threatening complication where additional transfusion can worsen anemia; suspect when post-transfusion Hb drops below the pre-transfusion level with reticulocytopenia
- Fibrinogen is the first factor to reach critically low levels during massive hemorrhage; monitor closely and replete with cryoprecipitate or fibrinogen concentrate
- Viscoelastic testing (TEG/ROTEM) enables targeted, goal-directed transfusion therapy in massive hemorrhage and reduces unnecessary blood product use

## References
1. Carson JL, et al. Transfusion thresholds and other strategies for guiding allogeneic red blood cell transfusion. Cochrane Database Syst Rev. 2016;10:CD002042.
2. Delaney M, et al. Transfusion reactions: prevention, diagnosis, and treatment. Lancet. 2016;388(10061):2825-2836.
3. Holcomb JB, et al. Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs. 1:1:2 ratio and mortality in patients with severe trauma (PROPPR). JAMA. 2015;313(5):471-482.
4. Vlaar APJ, et al. Transfusion-related acute lung injury (TRALI): a clinical review. Lancet. 2013;382(9896):984-994.
5. Slichter SJ. Platelet transfusion therapy. Hematol Oncol Clin North Am. 2007;21(4):697-729.