Hemoglobin Increase from One Unit of Blood Transfusion
One unit of packed red blood cells (PRBCs) increases hemoglobin by approximately 1 g/dL in an average-sized adult who is not actively bleeding. 1
Standard Expected Response
- Each 300 mL unit of PRBCs typically raises hemoglobin by 1 g/dL or hematocrit by 3% in normal-sized adults without concurrent blood loss 1
- This estimate applies specifically to patients who are hemodynamically stable and not experiencing ongoing hemorrhage 1
Important Modifying Factors
Pre-Transfusion Hemoglobin Level
- Lower baseline hemoglobin is associated with a greater hemoglobin rise per unit transfused 2
- In patients with subarachnoid hemorrhage, pre-transfusion hemoglobin explained an additional 12% of variance in post-transfusion response (P < 0.001) 2
- This relationship persisted after controlling for number of units, gender, and body mass index 2
Patient-Specific Variables
- Body mass index and gender influence the magnitude of hemoglobin increase, though pre-transfusion hemoglobin level appears to be the strongest predictor 2
- Larger patients may require more blood volume to achieve the same hemoglobin increment 1
Clinical Implications
Single-Unit Transfusion Strategy
- One unit of PRBCs is likely sufficient for most hemoglobin targets, especially in patients with more severe anemia 2
- Transfusion at lower hemoglobin levels may be relatively more cost-effective given the greater hemoglobin rise per unit 2
Timing of Iron Availability
- The iron contained in transfused red cells (147-278 mg per unit) is NOT immediately available for erythropoiesis 1
- Transfused red cells have an average lifespan of 100-110 days, and iron is only released after phagocytosis 1
- In anemia of inflammation, iron recycling may take even longer due to sequestration in macrophages 1
Common Pitfalls
- Do not assume transfusion corrects iron deficiency: Pre-transfusion iron indices should be obtained, as supplemental iron therapy may be needed in the 90 days following transfusion if the underlying anemia stemmed from iron deficiency 1
- Avoid routine two-unit transfusions: The traditional practice of transfusing two units may be unnecessary, particularly in patients with lower baseline hemoglobin who demonstrate greater per-unit responses 2
- Consider plasma volume expansion: In heart failure and chronic liver disease patients, apparent anemia may reflect increased plasma volume rather than true hemoglobin deficiency, making the standard 1 g/dL increment less predictable 3