Evaluation of the Sysmex XN automated hematopoietic progenitor cell enumeration for timing of peripheral blood stem cell harvest

Background: Enumeration of stem cells is essential in the management of peripheral blood stem cell (PBSC) harvest. An alternative to the gold standard flow cytometric CD34+ stem cell count is the fully automated hematopoietic stem cell (HPC) count on the Sysmex XN hematology analyzer.

Materials and methods: Eighty-nine patients and healthy stem cell donors who underwent PBSC harvest were included in the study. Stem cells were enumerated in pre-harvest peripheral blood and the apheresis yield by both flow cytometric CD34+ stem cell enumeration and by the Sysmex XN HPC count.

Results: The Sysmex HPC concentration overestimated the CD34+ stem cell concentration by a ratio of 1.3 in average. The agreement between the two methods was poor at concentration <40 stem cells/μL (Bias: 45 %, 95 % limits of agreement: -71 - 160 %). CD34+ stem cell concentration and HPC concentration correlated well in pre-harvest peripheral blood (R=0.73, slope=0.96). We established a positive cut off >43.5 HPC/μL, where PBSC harvest can be initiated. And a negative cut off <16.5 HPC/μL, where harvest should be postponed or other mobilizing regimens or bone marrow harvest should be considered. 33 % of measurements were in between the negative and positive cut-off and would require a supplementary CD34+ cell count.

Conclusion: Although Sysmex HPC count correlates well with CD34+ cell count in peripheral blood, the agreement between the two methods is poor, especially at low concentrations, namely in the clinical decision range. Sysmex HPC count as a surrogate for CD34+ cell count should, therefore, be used with caution.