Assessment of haematopoietic progenitor cell counting with the Sysmex® XN-1000 to guide timing of apheresis of peripheral blood stem cells

Abstract

Background: Successful peripheral blood stem cell (PBSC) collection depends on optimal timing of apheresis, as usually determined by flow cytometry CD34-positive (⁺) cell count in peripheral blood (PB). Since this method is costly and labour-intensive, we evaluated the use of the Hematopoietic Progenitor Cell count programme on a Sysmex^® XN haematologic analyser (XN-HPC) as a rapid and inexpensive alternative for predicting CD34⁺ cell count in PB samples.

Materials and methods: Haematopoietic progenitor cell and CD34⁺ cell counts were compared using 273 PB samples collected from 78 healthy donors and 72 patients who underwent PBSC transplantation. We assessed the effectiveness of the XN-HPC in safely predicting pre-harvest CD34⁺ counts. The most efficient cut-off values of XNHPC were identified. We also evaluated the imprecision (coefficient of variation, CV) and functional sensitivity.

Results: Imprecision of the XN-HPC count was <6.3% on daily measurement of three levels of quality control material. Functional sensitivity was 8.9×10⁶/L. A cut-off value of ≥62×10⁶/L XN-HPC for multiple myeloma (MM) patients and ≥30×10⁶/L for all other subjects had both 100% specificity and 100% positive predictive value for identifying samples with CD34⁺ cells ≥20×10⁶/L. An XN-HPC threshold of <13×10⁶/L identified preharvest CD34⁺ cell count <10×10⁶/L with 100% sensitivity and 100% negative predictive value.

Discussion: The XN-HPC is a fast, easy and inexpensive test that can safely improve apheresis workflow thus possibly replacing other more expensive CD34 counts currently performed and promoting optimal timing of PBSC collection.

Figure 1

Correlation of the Sysmex XN haematologic XN-HPC analyser and CD34-positive (⁺) cells count by Passing-Bablok regression analysis. Solid and dashed lines represent the regression line and 95% Confidence Interval (CI) of the slope, respectively. Grey line represents the identity line (y=x). Correlations between XN-HPC and CD34⁺ cells are shown for (A) all the 273 peripheral blood (PB) samples, (B) healthy donors (n=97), (C) lymphomas (n=82), (D) multiple myeloma (n=83). See Table II for data of Passing-Bablok regression analysis.

Figure 2

CD34-positive (⁺) and kinetics of the Sysmex^® XN haematologic XN-HPC analyser showing CD34⁺ (white squares) and XN-HPC (black circles) cell count performed on successive days starting initiation of mobilisation. Counts are expressed as means ± 1 Standard Error of Mean. Kinetics are shown for (A) 15 lymphomas, 1 Ewing sarcoma, 1 neuroblastoma patient, and (B) 13 multiple myeloma patients.