When should packed red blood cells (PRBC) be transfused, what hemoglobin thresholds apply for adults and children, and what is the typical dosing?

Packed Red Blood Cell Transfusion: Thresholds, Indications, and Dosing

For most hemodynamically stable adults, transfuse packed red blood cells when hemoglobin falls below 7 g/dL; patients with cardiovascular disease should receive transfusion at ≤8 g/dL, and those with acute coronary syndrome or traumatic brain injury may benefit from a threshold of <10 g/dL and <9 g/dL respectively. 1, 2

Hemoglobin-Based Transfusion Thresholds

General Adult Population (Hemodynamically Stable)

• Transfuse when hemoglobin <7 g/dL – this restrictive strategy is supported by Level 1 evidence from multiple high-quality randomized controlled trials and is as effective as liberal strategies (targeting 10 g/dL) without increasing mortality or morbidity. 1, 2, 3
• Do NOT transfuse when hemoglobin >10 g/dL – liberal transfusion strategies provide no clinical benefit and significantly increase risks of transfusion-related acute lung injury (TRALI), transfusion-associated circulatory overload (TACO), nosocomial infections, and multi-organ failure. 1, 2, 3
• Hemoglobin <6 g/dL almost always requires transfusion, particularly when anemia is acute, as compensatory mechanisms are maximally stressed and tissue hypoxia is imminent. 2, 4

Patients with Cardiovascular Disease

• Transfuse at hemoglobin ≤8 g/dL for patients with coronary artery disease, heart failure, or peripheral vascular disease, as these patients have reduced physiologic tolerance to anemia. 1, 2, 5
• This higher threshold is recommended by the 2025 EACTS/EACTAIC/EBCP guidelines and supported by high-quality evidence. 1, 2

Acute Coronary Syndrome

• Transfuse when hemoglobin <10 g/dL – the 2025 MINT trial demonstrated superior outcomes with this liberal strategy in patients with acute myocardial infarction. 2
• For symptomatic patients with acute coronary syndrome and hemoglobin <8 g/dL, transfusion should be strongly considered. 1, 2, 5

Traumatic Brain Injury

• Transfuse at hemoglobin <9 g/dL – the 2025 TRAIN trial showed improved 6-month neurological outcomes, better motor function scores, and higher quality-of-life ratings with this liberal strategy compared to the restrictive 7 g/dL threshold. 2

Critically Ill and Mechanically Ventilated Patients

• Transfuse when hemoglobin <7 g/dL for resuscitated trauma patients and those on mechanical ventilation, as liberal strategies provide no additional benefit in these populations. 1, 3, 6

During Cardiopulmonary Bypass (CPB)

• Transfuse when hematocrit <18% (hemoglobin ~6.0 g/dL) during CPB – this is a Class I recommendation. 1
• For hematocrit 18-24%, consider transfusion based on oxygen delivery (DO₂ >273 mL/min/m² should be maintained) and cerebral oximetry. 1
• Do NOT transfuse when hematocrit >24% if oxygen delivery and extraction are acceptable. 1

Clinical Indications Beyond Hemoglobin Level

Never use hemoglobin level alone as a transfusion trigger – the decision must incorporate multiple clinical parameters. 1, 3, 6

Absolute Indications (Transfuse Regardless of Hemoglobin)

• Hemorrhagic shock or hemodynamic instability: symptomatic hypotension, persistent tachycardia unresponsive to fluids, evidence of shock, or inadequate oxygen delivery. 2, 3, 6
• Active ongoing hemorrhage with signs of volume depletion. 1, 6

Symptom-Driven Triggers

Transfusion is indicated when any of the following occur, independent of hemoglobin value: 2, 3

• Chest pain or angina
• New ST-segment changes on ECG
• Tachycardia >110 bpm unresponsive to fluid resuscitation
• Orthostatic hypotension or syncope
• Severe dyspnea or tachypnea
• Altered mental status or confusion
• Elevated lactate or metabolic acidosis
• Low mixed-venous oxygen saturation (SvO₂)
• Oliguria or decreased urine output

Assessment of Oxygen Delivery

• Evaluate intravascular volume status, evidence of shock, duration and acuity of anemia, and cardiopulmonary reserve when making transfusion decisions. 1, 3, 6
• During CPB, transfusion is effective when SvO₂ <68% and/or oxygen extraction ratio >39%. 1

Transfusion Dosing and Administration Protocol

Standard Dosing

• One unit of packed red blood cells contains approximately 300 mL with a hematocrit of 50-80%, containing 42.5-80 g of hemoglobin or 128-240 mL of pure RBCs. 1
• Expected hemoglobin increase: 1-1.5 g/dL per unit in a normal-sized adult without ongoing blood loss. 1, 2, 3
• In patients with lower baseline hemoglobin, the rise per unit may be greater due to improved oxygen-carrying capacity utilization. 7

Administration Protocol

• Administer one unit at a time in the absence of acute hemorrhage. 1, 2, 3
• Reassess clinical status and hemoglobin after each unit before administering additional units – this single-unit approach reduces unnecessary exposure and allows timely clinical evaluation. 1, 2, 3
• Hemoglobin equilibrates rapidly – measurements taken 15 minutes post-transfusion correlate excellently with 24-hour values in normovolemic patients recovering from acute bleeding. 8

Special Population Considerations

Cancer and Chemotherapy-Induced Anemia

• Classify patients into three categories: (1) asymptomatic without significant comorbidities (observation appropriate), (2) asymptomatic with comorbidities or high risk (consider transfusion), and (3) symptomatic (transfusion indicated). 1
• Consider transfusion even in asymptomatic patients if progressive hemoglobin decline occurs after anticancer treatment. 1
• The major benefit is rapid correction of anemia when immediate intervention is required during myelosuppressive chemotherapy. 1

Patients with Chronic Kidney Disease

• Target hemoglobin of 11.0-12.0 g/dL with erythropoiesis-stimulating agents for chronic management, but acute transfusion is still needed at critically low levels (e.g., <7 g/dL). 2

Pediatric Patients

• The evidence provided focuses primarily on adult populations; pediatric thresholds may differ and should be guided by pediatric-specific guidelines. 1, 2

Critical Pitfalls and Risks to Avoid

Risks of Liberal Transfusion

• Transfusion-related acute lung injury (TRALI) is a leading cause of transfusion-associated morbidity and mortality. 1, 2, 3
• Transfusion-associated circulatory overload (TACO) and pulmonary edema, particularly in patients with heart failure. 2, 6
• Increased nosocomial infections – transfusion is independently associated with higher infection rates. 1, 3
• Multi-organ failure and systemic inflammatory response syndrome (SIRS). 3
• Venous and arterial thromboembolism – analysis of cancer patients showed increased odds ratios of 1.60 and 1.53 respectively. 1
• Increased mortality – liberal strategies are associated with higher mortality without improving outcomes. 1, 3

Common Clinical Errors

• Fixating on hemoglobin numbers alone without considering clinical context, symptoms, comorbidities, and oxygen delivery parameters. 1, 3, 5
• Automatically ordering "2 units of PRBCs" – this outdated practice is potentially harmful; modern guidelines favor single-unit transfusion with reassessment. 2
• Transfusing to achieve hemoglobin >10 g/dL – this provides no benefit and increases complications across all patient populations except acute coronary syndrome and traumatic brain injury. 1, 2, 3
• Delaying assessment of underlying causes – address nutritional deficiencies, occult bleeding, and chronic disease rather than defaulting to transfusion. 3

Transfusion-Related Infections

• Modern screening has dramatically reduced infectious risks since 1984, but risks remain: HIV (1:1,467,000), HCV (1:1,149,000), HBV (1:282,000-357,000). 2
• Prestorage leukoreduction decreases febrile nonhemolytic transfusion reactions, the most common adverse reaction. 1

Iron Overload

• Transfusion-related iron overload occurs in patients requiring frequent transfusions over several years (e.g., myelodysplastic syndrome), but is unlikely during short-term chemotherapy (<1 year). 1

Exceptions and Special Circumstances

Religious Refusal

• The only recognized situation where transfusion is withheld at critically low hemoglobin (e.g., 4.8 g/dL) is documented patient refusal based on religious beliefs (e.g., Jehovah's Witnesses). 2
• Maximize alternative therapies: intravenous iron, erythropoiesis-stimulating agents, supplemental oxygen, and strategies to minimize further blood loss. 2

Antithrombin Deficiency During CPB

• Use antithrombin concentrate as primary treatment to improve heparin sensitivity (Class I recommendation). 1
• If antithrombin concentrate is unavailable, fresh frozen plasma should be considered, but prophylactic FFP to reduce perioperative blood loss is not recommended. 1