Calculating Volume to be Collected During Apheresis
The volume of blood to be processed during apheresis is calculated using the formula: BV = ((Target cells in product) / (Pre-apheresis cell concentration × Collection Efficiency)) × 100, where collection efficiency (CE2) typically ranges from 48-53% for most procedures 1, 2.
Key Formula Components
1. Total Blood Volume (TBV) Estimation
- Standard calculation: 70 mL/kg body weight 3
- This serves as the baseline for determining how many blood volumes to process
- Critical caveat: Standard formulas may significantly over- or underestimate TBV in obese patients (BMI >30), requiring modified approaches 4
2. Collection Efficiency (CE2)
The CE2 represents the percentage of target cells actually collected from processed blood:
- Allogeneic donors: 53% ± 17% 1
- Patients overall: 48% ± 15% 1
- Disease-specific variations 1:
- Multiple myeloma: 48% ± 15%
- Non-Hodgkin lymphoma: 48% ± 15%
- Hodgkin's lymphoma: 42% ± 13% (significantly lower)
3. Standard Processing Volume
For platelet apheresis: Processing 4,000-5,000 mL of donor blood over 1.5-2 hours yields a product containing platelets equivalent to 6-9 units of whole blood-derived platelets 5.
Practical Calculation Algorithm
Step 1: Determine Target Cell Dose
- For CD34+ cell collection: Calculate target CD34+ cells/kg for the recipient
- For platelet collection: Minimum 3 × 10¹¹ platelets per apheresis unit 5
Step 2: Measure Pre-Apheresis Cell Concentration
- CD34+ cells/μL in peripheral blood (for stem cell collection)
- Platelet count (for platelet apheresis)
Step 3: Apply the Formula
BV = ((Target cells) / (Pre-apheresis concentration × CE2)) × 100 1, 6
Where:
- BV = blood volume to process (mL)
- CE2 = 0.48-0.53 (use disease-specific values when available)
- Adjust CE2 downward for Hodgkin's lymphoma patients
Step 4: Validate Against Safety Limits
- Maximum safe processing: Generally 3× TBV in a single session 2
- Extracorporeal volume considerations: Ensure patient can tolerate the volume outside their circulation
- Processing less than 3× TBV is often sufficient when calculations are optimized 2
Clinical Implementation
The formula has been validated with strong correlation (r = 0.89, p < 0.0001) between predicted and actual CD34+ cell collection 1. Implementation of calculated approaches versus standard "3× TBV" protocols has demonstrated:
- Reduced need for multiple apheresis sessions in patients <60 years
- Optimized procedure times
- Greater blood volume processed in patients when needed
- Less blood volume processed in allogeneic donors when appropriate 1
Critical Pitfalls to Avoid
Don't assume all patients require 3× TBV processing - this is often excessive and unnecessarily prolongs procedures 2
Account for disease-specific collection efficiencies - Hodgkin's lymphoma patients have significantly lower CE2 and will require more blood volume processed 1
Verify your institution's apheresis product splitting practices - many centers now split collections into 2-3 products rather than single units, affecting dose calculations 5
In obese patients (BMI >30), standard TBV formulas fail - consider modified Lemmens-Bernstein (LB-60) for women or modified Gilcher's Rule (Gilchers-65) for men 4
Volume determination methods vary - apheresis instrument calculations versus specific gravity methods show 96.6% agreement, but verify your institution's standard 7
Quality Control
Calculate CE2 for each procedure to:
- Compare device performance
- Assess operator technique
- Predict future collection needs
- Optimize resource utilization 2
The ability to accurately calculate minimum blood volume eliminates unnecessary procedure time, reduces donor/patient burden, and improves cost-effectiveness 6.