(P-BT-8) Analysis of Methods for Quantification of White Blood Cell Counts for Processing Hematopoietic Progenitor Cell Apheresis Products

Background/Case Studies: Processing hematopoietic progenitor cell (HPC) apheresis products necessitate an accurate white blood cell (WBC) count to determine appropriate freezing concentrations and to optimize cell viability. This study compares the efficacy and validity of two primary methods for WBC quantification. Our flow cytometry laboratory employs a BD FACSLyric Flow Cytometry System (FC BD; BD Biosciences, Franklin Lakes, NJ) to identify CD45-positive cells. Our hematology laboratory utilizes a Sysmex XN-10 Automated Hematology Analyzer (HEME Sysmex; Sysmex Corp., Kobe, Japan) for automated WBC counts. The goal of this study was to assess and validate use of the HEME Sysmex for enumerating WBCs in HPC apheresis products.

Study

Design/Methods: A two-year historical data analysis was conducted comparing total WBC counts from FC BD versus HEME Sysmex analyzer for 72 HPC apheresis product samples. Statistical analyses included calculation of coefficient of variation (CV) and linear regression including slope and coefficient of determination (R²).

Results/Findings: We observed that 90% of samples exhibited < 15% difference between the two methods. Upon further investigation of samples with >15% variation, 57% of these (4/7) had counts ≥ 3.0x10⁵ WBC/µL. It is well-documented that HPC apheresis products typically contain higher concentrations of cells and are often more viscous than whole blood, thus increasing the risk of undercounting WBCs by the HEME Sysmex. The average CV was 6%, indicating acceptable precision. The calculated slope was 0.9073 and R² was 0.9786, demonstrating a significant direct linear relationship between the two methods of WBC enumeration (Figure A).

Conclusions: This analysis led to a Situation, Background, Assessment, and Recommendation (SBAR) being generated to evaluate the methods described above. Ultimately, it was determined that use of the automated HEME Sysmex for WBC quantification in HPC apheresis products was satisfactory for our laboratory’s workflow needs. Additional procedural modifications were implemented to optimize accuracy, including decreasing the acceptable upper WBC concentration for HPC apheresis product samples from 4.4x10⁵cells/µL to 3.0x10⁵ cells/µL, performing a 1:7 manual dilution for samples >3.0x10⁵ WBC/µL, and analyzing samples in duplicate with an allowable replicate variation of ±3%.