What hemoglobin or hematocrit level and clinical criteria define the cutoff for whole‑blood (or packed red‑cell) transfusion in a patient with dengue?

Transfusion Cutoff for Dengue Patients

In dengue patients, transfuse packed red blood cells when hemoglobin falls below 7 g/dL in hemodynamically stable patients, or immediately at any hemoglobin level if there is active bleeding with hemodynamic instability (systolic BP <90 mmHg or heart rate >110 bpm), prolonged shock, or a rapidly falling hematocrit despite adequate fluid resuscitation. 1

Hemoglobin-Based Transfusion Thresholds

Standard Threshold for Stable Patients

• Apply the general restrictive transfusion threshold of hemoglobin <7 g/dL (70 g/L) for hemodynamically stable dengue patients without active bleeding 1
• This threshold is supported by high-quality evidence showing no difference in mortality or morbidity compared to liberal strategies (Hb 9-10 g/dL) 1
• For patients with preexisting cardiovascular disease, use a slightly higher threshold of hemoglobin <8 g/dL 1

Critical Threshold Requiring Immediate Transfusion

• Transfusion is almost always indicated when hemoglobin falls below 6 g/dL, particularly when anemia develops acutely 1, 2
• At hemoglobin ≤4.8 g/dL (3 mmol/L), immediate transfusion is mandatory unless explicit patient refusal exists, as compensatory mechanisms are maximally stressed and tissue hypoxia is imminent 2

Clinical Criteria Overriding Hemoglobin Thresholds

Immediate Transfusion Indicators (Regardless of Hemoglobin)

Transfuse immediately if any of the following are present, even if hemoglobin is above 7 g/dL:

• Active bleeding with hemodynamic instability: systolic BP <90 mmHg or heart rate >110 bpm 1
• Prolonged or repeated shock despite adequate fluid resuscitation 3
• Rapidly falling hematocrit (>20% drop) with ongoing plasma leakage 4, 3
• Signs of inadequate oxygen delivery: elevated lactate, low pH, low central/mixed venous oxygen saturation 1
• Symptomatic anemia: chest pain, severe dyspnea, altered mental status, or orthostatic symptoms unresponsive to fluids 1, 5

Dengue-Specific Risk Factors for Hemorrhage

Monitor closely and have a lower threshold for transfusion in patients with:

• Gastrointestinal bleeding, which significantly correlates with transfusion requirements in dengue (p<0.0001) 4
• Duration of shock: each hour of shock increases hemorrhage risk (OR 2.11) 3
• Low-normal hematocrit at time of shock (OR 0.72 per percentage point decrease), indicating prior blood loss 3
• Dengue shock syndrome (DHF grades III-IV) with severe coagulopathy and platelet dysfunction 6

Critical Pitfall: Hematocrit Interpretation in Dengue

The hematocrit may remain falsely elevated despite significant blood loss due to hemoconcentration from plasma leakage, which is pathognomonic for dengue hemorrhagic fever. 1, 6

• A "normal" or even elevated hematocrit does NOT exclude the need for transfusion in actively bleeding dengue patients 1
• Conversely, a low-normal hematocrit during shock is paradoxical and suggests occult hemorrhage requiring immediate transfusion 3
• Serial hematocrit measurements are essential: a rapid drop (>20%) indicates active bleeding even if absolute values remain in normal range 4, 3

Transfusion Protocol for Dengue

Administration Strategy

• Transfuse one unit of packed red cells at a time in the absence of massive hemorrhage 1, 5
• Reassess clinical status and hemoglobin after each unit before administering additional units 1, 5
• Each unit should increase hemoglobin by approximately 1-1.5 g/dL 2

Blood Component Selection

The choice of blood components in dengue depends on the clinical scenario:

• Packed red cells (47% of transfusions): for rapid hematocrit drop or hemoglobin <7 g/dL 4
• Platelet concentrate (64.7% of transfusions): for active bleeding, NOT based on platelet count alone (platelet count does not correlate with transfusion requirement, p=0.207) 4
• Fresh frozen plasma (29.4% of transfusions): for circulatory failure unresponsive to IV fluids, or significant coagulopathy with bleeding 4, 6

Massive Transfusion Considerations

For dengue patients with massive hemorrhage (>50% blood volume in <3 hours or >150 mL/min):

• Activate massive transfusion protocols 1
• Prevent hypothermia, acidosis, and hypocalcemia (maintain ionized calcium >1.0 mmol/L) 1
• Use point-of-care testing to guide hemostatic resuscitation 1

Important Caveats

Platelet Count Is NOT a Transfusion Trigger

• Platelet count does not correlate with transfusion requirements in dengue (p=0.207) 4
• Transfuse platelets only for active bleeding, not prophylactically based on count alone 4

Avoid Over-Transfusion

• Do not transfuse when hemoglobin is >10 g/dL, as this increases risks of transfusion-related acute lung injury (TRALI), infections, and circulatory overload without benefit 2, 5
• Liberal transfusion strategies provide no mortality benefit and may worsen outcomes 1

Communication with Blood Bank

• Physicians should communicate anticipated transfusion needs to the blood bank in advance for dengue patients with warning signs or severe dengue 4
• Approximately 10.6% of dengue hemorrhagic fever patients require blood component therapy 4