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.