(P-BC-52) Residual WBC (rWBC) Enumeration in Blood Products Using a Hematology Analyzer

To meet AABB standards, leukoreduced (LR) blood products must contain < 5x10⁶ rWBC per component. The European Union standard is < 1x10⁶ rWBC/component. Enumeration of rWBC has been routinely performed using the ADAM rWBC instrument (Nanoentek). The Sysmex hematology analyzer (XN-1000) in Blood Bank (BB) mode can perform rWBC counts on red blood cell (RBC) and platelet (PLT) components (FDA clearance 2022). The device is currently not approved for rWBC enumeration in whole blood (WB) products. As part of the Sysmex device validation, rWBC enumeration using the ADAM versus Sysmex was performed using routine blood center quality control samples of RBC, PLT, and WB products.

Study

Design/Methods:

The validation of the Sysmex XN-1000BB assessed linearity, precision, accuracy, carryover, and limits of quantification (LOQ) and detection (LOD). Prespecified acceptance criteria for linearity were r²>0.95, for precision CV<20%, for accuracy 80% of measured values had to be within 20% of expected values, LOQ is the lowest concentration where CV≤20%, LOD is the lowest conc. where 95% CI of mean does not overlap with 95% CI of LR sample and carryover had to be <1%. For RBC and WB samples (N=6 each), non-LR components were serially diluted with LR products. Apheresis platelet (PLT) samples (N=6) were spiked with ABO matched WBCs isolated from Trima LR system chambers (Terumo BCT). In addition, samples from routine quality control (QC) ADAM testing were run on the Sysmex. QC results were considered discrepant when rWBC passed (< 5x10⁶) or failed ( >5x10⁶) on one device and not the other. Flow cytometry enumeration was performed on a BD FACSLyric flow cytometer with the BD Leukocount Kit.

Results/Findings:

Sysmex rWBC counts passed linearity ranging from 0-100 WBC/μL for RBCs and PLTs, and 0-6000 WBC/μL for WB. Precision passed >2.3, >9.3 or >3.7 WBC/ μL for RBCs, PLTs and WB, respectively. LODs were < 1/μL, however LOQ were higher and identical to precision cutoffs. Carryover was < 0.11% in all sample types. No discrepancies between Sysmex and ADAM QC results for RBC were detected. In contrast, Sysmex rWBC results were lower than ADAM for 6 PLT units and higher than ADAM for 1 PLT and 6 WB units (Table 1). Flow cytometry confirmatory testing supported ADAM results (4 PLT, and 4 WB).

Conclusions:

The Sysmex passed all aspects of the validation except for the QC sample comparison in PLT and WB samples. Sysmex provided an official notification of potential interference due to processing variables for RBC and PLT samples leading to increased rWBC counts. Such interference occurs in the white blood cell differential, PLT and/or RBC fluorescent scattergrams and was observed in our evaluation in WB products and a one PLT product.