PRBC vs PCV: Key Distinctions
PRBC (Packed Red Blood Cells) is a blood product used for transfusion, while PCV (Packed Cell Volume) is a laboratory measurement—they are fundamentally different entities that should never be confused in clinical practice.
PRBC: The Blood Product
Packed Red Blood Cells refers to the actual transfusion component prepared from whole blood after plasma removal 1, 2:
- Composition: Each unit contains approximately 300 mL of concentrated red blood cells with minimal plasma 1
- Preparation: Created by centrifugation of whole blood to separate and remove most plasma, leaving concentrated RBCs 1
- Clinical use: Administered to correct anemia and improve oxygen-carrying capacity in blood 1
- Expected effect: One unit typically raises hemoglobin by 1 g/dL or hematocrit by 3% in normal-sized adults without ongoing blood loss 1, 2
Administration Requirements
- Must be crossmatched before transfusion to confirm ABO compatibility 2
- Should be transfused one unit at a time with clinical reassessment after each unit 2, 3
- Requires vital sign monitoring at baseline, 15 minutes after starting, and at completion 2, 4
PCV: The Laboratory Measurement
Packed Cell Volume (also called hematocrit) is a laboratory test that measures the percentage of blood volume occupied by red blood cells 5:
- What it measures: The ratio of red cell volume to total blood volume, expressed as a percentage 5
- Clinical interpretation: Reflects both red cell volume AND plasma volume—not just red cell mass 5
- Key limitation: PCV is a fluctuating ratio of variable numbers because plasma volume and red cell volume can vary independently 5
- Normal values: Varies by patient population, but transfusion is typically considered when hemoglobin falls below 7-8 g/dL (corresponding to PCV of approximately 21-24%) 3, 4
Critical Pitfall to Avoid
PCV does not directly reflect total oxygen-carrying capacity because it can be artificially elevated by dehydration (low plasma volume) or artificially lowered by fluid overload (high plasma volume), even when the actual red cell mass remains unchanged 5. This is why red cell volume (RCV) is considered a more reliable indicator of oxygen transport capacity than PCV 5.
Clinical Context: How They Relate
When you transfuse PRBC, you monitor the effect by measuring PCV (or hemoglobin) before and after transfusion 2, 6:
- Pre-transfusion PCV influences response: Lower starting PCV is associated with greater rise in PCV per unit transfused 6
- Monitoring strategy: Check PCV/hemoglobin after each unit to guide further transfusion decisions rather than ordering multiple units simultaneously 2, 3
- Transfusion at lower hemoglobin levels may be more cost-effective since each unit produces a larger increment 6