The New Sysmex XN-2000 Automated Blood Cell Analyzer More Accurately Measures the Absolute Number and the Proportion of Hematopoietic Stem and Progenitor Cells Than XE-2100 When Compared to Flow Cytometric Enumeration of CD34+ Cells

The gold standard to count circulating hematopoietic stem and progenitor cells (HPCs) is to enumerate CD34 cells by using flow cytometry [1, 2]. XE-2100 (Sysmex, Kobe, Japan), a currently used hematology analyzer, can be used to quantify HPCs, generating counts that reportedly correlate with those obtained using flow cytometric analysis of CD34 cells; however, XE-2100 HPC counts were 1.86-fold higher than those calculated by flow cytometry [3]. The recently launched XN-2000 (Sysmex) can also be used to quantify HPCs, but its performance on HPC counts has not been evaluated. We assessed the HPC counting performance of XE-2100 and XN-2000 and compared them to CD34 cell counts by flow cytometry. A total of 120 peripheral blood samples collected from 31 patients who had undergone stem cell transplantation (SCT) at Asan Medical Center, Seoul, Korea between June 2013 and October 2013 were randomly selected. The CD34 cell proportion (%) was measured in each sample by using flow cytometric enumeration of CD34 HPCs [1], performed using FACScanto II (Becton-Dickinson, Sunnyvale, CA, USA) and phycoerythrin (PE)-conjugated CD34 and fluorescein isothiocyanate (FITC)conjugated CD45 (Becton-Dickinson). CD34 cell numbers obtained using XE-2100 and XN-2000 analyzers were calculated by multiplying their respective white blood cell (WBC) counts with their CD34 cell proportion (%). As a reference for the HPC counts, the CD34 cell counts, defined as the means of XE2100 and XN-2000 CD34 cell numbers, were generated. HPC numbers and proportion (%) were measured by both XE-2100 (immature myeloid information [IMI] channel, XE-2100 HPC numbers, and proportion [%]) and XN-2000 (white precursor cell [WPC] channel, XN-2000 HPC numbers and proportion