Method comparison between hematopoietic progenitor cell and CD34+ cell counts in hematopoietic stem cell collection.

Background: The reference method for hematopoietic stem cell enumeration is flow cytometric CD34+ cell analysis. We evaluated using the hematopoietic progenitor cell (HPC) count on the Sysmex hematology analyzer to safely replace some flow cytometric measurements performed in peripheral blood samples to guide apheresis timing.

Study design and methods: We compared HPC and CD34+ cell counts in 133 preharvest peripheral blood samples and 124 apheresis products.

Results: Pre-apheresis HPC counts ≥24 × 10⁶/L in healthy donors and ≥36 × 10⁶/L in lymphoma patients predicted adequate mobilization with 100% specificity and positive predictive value, saving 79% and 63% of flow cytometry analyses, respectively. Due to a positive bias (mean bias 50.26; 95% CI 36.24-64.29), a higher threshold was needed in multiple myeloma patients (HPC $\ge$ 132 × 10⁶/L), saving only 24% of flow cytometry analyses.

Conclusion: When the HPC count is above the corresponding threshold, apheresis could be safely initiated without waiting for the flow cytometry result, thereby reducing time-to-decision. Lower HPC values, however, require confirmation by flow cytometry.