Volume of One Unit of Packed Red Blood Cells
One unit of packed red blood cells (PRBCs) contains approximately 300 mL. 1, 2, 3
Standard Unit Volume
A standard adult unit of PRBCs is typically 300 mL in volume, which is the accepted reference for calculating expected hemoglobin increases and transfusion effects 1, 2, 3
Some sources reference units ranging from 300-400 mL, but 300 mL represents the standard unit size used in clinical practice 1, 4
Blood collection packs are manufactured to collect approximately 450 mL ± 10% of whole blood, which after processing yields approximately 300 mL of packed red cells 1
Clinical Implications of Unit Volume
Expected Hemoglobin Response
Each 300 mL unit of PRBCs typically raises hemoglobin by 1 g/dL or hematocrit by 3% in normal-sized adults without ongoing blood loss 2, 3
This translates to approximately 1.9% ± 1.2% hematocrit increase per unit based on actual clinical data, though the traditional "3% rule" assumes a larger 500 mL unit 4
Pediatric Dosing Considerations
- In pediatric patients, PRBCs are dosed at 10-15 mL/kg, meaning a 22 kg child would receive 220-330 mL, which approximates one standard adult unit 5
Important Caveats
Variability exists in actual unit volumes depending on the donor and collection method, with some units containing up to 400 mL 1
The anticoagulant-to-blood ratio must be maintained during collection, which is why appropriately sized collection packs (450 mL or 250 mL) are selected 1
When calculating transfusion effects, always consider that patient size, ongoing blood loss, and hemodilution significantly affect the actual hemoglobin increment achieved 3, 4