BACKGROUND: The outcome of peripheral blood stem cell (PBSC) harvest depends on mobilization and leukapheresis. Some poor harvests might not be directly related to poor mobilizations.

STUDY DESIGN AND METHODS: We retrospectively analyzed the results of 793 consecutive healthy donors who underwent PBSC donation to evaluate the impact of low mean corpuscular volume (MCV) of red blood cells on the outcomes of hematopoietic stem cell mobilization and leukapheresis.

RESULTS: The circulating CD34+ cells in peripheral blood after five doses of granulocyte–colony-stimulating factor injection were similar in donors with low MCV and those with normal MCV (68.0 × 106/L vs. 69.2 × 106/L, p = 0.38). The procedural settings were not different between the two groups. However, the apheresis outcome of donors with low MCV was significantly lower in total CD34+ cells, cell dose, apheresis yield, and collection efficiency than those with normal MCV (277.6 × 106 vs. 455.0 × 106; 4.9 × 106/kg vs. 8.2 × 106/kg; 16.9 × 106/L vs. 27.3 × 106/L; 0.285 vs. 0.388; all p < 0.0001). Similar results were noticed in subgroup analysis using the severity of microcytosis and Mentzer index for the donors with MCV of less than 80 fL. The collection efficiency was significantly correlated with the MCV (r = 0.30, p < 0.0001).

CONCLUSION: Low MCV was associated with poor apheresis outcomes in PBSC donors. This effect is not related to poor mobilization of CD34+ cells into the peripheral blood. Further studies to elucidate the detailed mechanism and develop strategy to avoid poor harvest are necessary.