What is the expected increase in hemoglobin (Hb) level in an average adult patient after transfusion of one unit of packed red blood cells (PRBCs)?

Expected Hemoglobin Increase from One Unit of Packed Red Blood Cells

One unit (300 mL) of packed red blood cells typically increases hemoglobin by 1 g/dL or hematocrit by 3% in a normal-sized adult without ongoing blood loss. 1, 2, 3

Standard Expected Response

• Each 300 mL unit of PRBCs raises hemoglobin by approximately 1 g/dL in hemodynamically stable adults 1, 2
• The equivalent hematocrit increase is 3% per unit 1, 2
• This estimate applies specifically to patients who are not experiencing concurrent hemorrhage or active bleeding 2

Important Modifying Factors That Affect Response

Pre-Transfusion Hemoglobin Level

• Lower baseline hemoglobin is associated with a greater hemoglobin rise per unit transfused 4
• In patients with subarachnoid hemorrhage, pre-transfusion hemoglobin explained an additional 12% of variance in post-transfusion response, with lower starting values producing larger increases 4
• This suggests transfusion at lower hemoglobin thresholds may be relatively more cost-effective 4

Patient Size and Body Habitus

• Larger patients require more blood volume to achieve the same hemoglobin increment 2
• Gender and body mass index (BMI) are recognized modifiers of transfusion response 4

Clinical Context and Underlying Disease

• In ICU patients, the mean hemoglobin increase per unit was only 0.45 g/dL (1.91 g/dL increase after average of 4.23 units over 7 days) 5
• Patients with internal medical disorders showed the lowest hemoglobin response (0.25 g/dL per unit) compared to other patient populations 5
• Critical illness, ongoing inflammation, and medical comorbidities can significantly blunt the expected hemoglobin rise 5

Pediatric Populations

• In children, 10 mL/kg of PRBCs increases hemoglobin by approximately 2.0 g/dL (20 g/L) 6
• For example, a 6.7 kg infant receiving 16.7 mL/kg would be expected to achieve approximately 3.34 g/dL hemoglobin rise 6

Clinical Implications and Reassessment

• Order exactly 1 unit at a time rather than multiple units simultaneously 3
• Reassess the patient clinically after each unit before deciding whether additional transfusion is needed 3
• No mandatory waiting period exists between units for stable patients—base decisions on clinical reassessment, not arbitrary time intervals 3
• Document baseline vital signs before transfusion and monitor at 15 minutes after starting and at completion 3

Common Pitfalls to Avoid

• Do not assume the "textbook" 1 g/dL rise applies universally—critically ill patients, those with internal medical disorders, and patients with higher baseline hemoglobin may have significantly lower responses 5, 4
• Do not assume transfusion corrects underlying iron deficiency—obtain pre-transfusion iron indices and provide supplemental iron therapy if needed in the 90 days following transfusion 2, 3
• The iron contained in transfused red cells (147-278 mg per unit) is NOT immediately available for erythropoiesis, as it is only released after phagocytosis over the 100-110 day lifespan of the transfused cells 2
• Be aware that PRBC transfusion carries risks including increased venous thromboembolism (OR 1.60), arterial thromboembolism (OR 1.53), and mortality (OR 1.34) in cancer patients 1, 3
• In critically ill patients, transfusion at a hemoglobin threshold of 7.0 g/dL was not associated with improved organ dysfunction compared to no transfusion, despite achieving hemoglobin increases of 0.7-2.4 g/dL 7