Expected Hemoglobin Rise Per mL of PRBC Transfusion in Children
The standard formula is: 10 mL/kg of packed red blood cells increases hemoglobin by approximately 2 g/dL (20 g/L) and hematocrit by approximately 6%. 1
Practical Calculation Formula
For calculating the required transfusion volume, use:
- Volume (mL) = Weight (kg) × Desired Hb increase (g/dL) × 3 / (Hematocrit of PRBC unit) 2
With standard UK PRBC units (hematocrit 0.6), this simplifies to the 10 mL/kg = 2 g/dL rule 2. This formula was validated in 379 pediatric transfusions with a correlation gradient of 5.02 between mL/kg transfused and Hb increase 2.
Key Clinical Points
Dosing Principles
- Always prescribe blood by volume (mL/kg) rather than units in pediatric patients 1
- The expected rise is consistent regardless of patient weight, age, starting hemoglobin, transfusion time, or sex 2
- Post-transfusion hemoglobin at 1 hour equals the value at 7 hours, so early checking is appropriate 2
Age-Specific Considerations
For premature neonates:
- Use a modified formula: Volume (mL) = 4/3 × Desired hematocrit rise × Weight (kg) 3
- This accounts for the higher blood volume per kilogram (70-100 mL/kg) in neonates 1
- Premature infants require CMV-negative blood components 1
For infants >3 months and children:
- The standard 10 mL/kg = 2 g/dL rule applies reliably 1
Important Caveats
Lower pre-transfusion hemoglobin produces greater rises per unit transfused 4. This means the formula may slightly overestimate the rise in patients with higher baseline hemoglobin and underestimate in severely anemic patients 4.
Monitor carefully for:
- Hypervolemia risk, especially with volumes >10-15 mL/kg 5
- Electrolyte imbalances during rapid transfusion 1
- Hypothermia, particularly in rapid transfusions 1
Exclude from calculations:
Transfusion Rate
Standard infusion rates of 10 mL/kg/h are safe and well-tolerated in children, allowing completion within 4 hours while optimizing patient and family time 6.