BACKGROUND Accurate quantification of hematopoietic stem cells (HSCs) collected during apheresis is essential for informing clinical decisions, including the optimal timing for discontinuation of collection, and in some cases discontinuation of mobilizing agents. In many collection centers, the product volume reported by the apheresis device is used to estimate the total cellular yield. However, a volume overestimation—particularly in the context of high CD34+ cell concentrations—may lead to premature discontinuation of mobilization protocols, potentially compromising the achievement of target CD34+ cell doses.

PATIENTS AND METHODS The analysis included 56 autologous apheresis procedures carried out among 15 adult patients at AORN Cardarelli and 20 pediatric patients at AORN Santobono-Pausilipon; 18 patients underwent 2 consecutive procedures. The apheresis procedures were performed with a Spectra Optia apheresis system (Terumo BCT, MNC program) following the manufacturer's protocol. The collection volume reported by the device (Vol_S) was compared with the volume measured by the processing facility (Vol_P) calculated using the formula: (Weight of the collected product – bag tare) / 1.05, where 1.05 is the specific gravity of the cellular products.

We computed:

Percent difference (Diff%) = (Vol_S – Vol_P) / Vol_P

Absolute difference (DiffAbs) = Vol_S – Vol_P

Clinical and procedural variables were analyzed to assess their impact on volume discrepancies:

Patient-related variables: peripheral blood WBC count, CD34+cell count, Plt count, MNC %, Hb, Hct and body weight of patient (PW).

Procedure-related variables: whole blood processed (BP), run time and flow rate.

The Mann-Whitney U test was used to assess differences between Vol_S and Vol_P. Pearson's correlation coefficient (cor.test function in R) was used to evaluate linear associations. Multiple linear regression analysis (lm function in R) was conducted to investigate the effect of collection center, age, and sex on Diff% and DiffAbs. To confirm the independence of observed associations, a secondary correlation analysis was performed on the residuals of the regression model.

RESULTS Vol_S and Vol_P differed significantly (p=1e-05). Mean Vol_S was 156 mL while mean Vol_P was 138 mL. The mean Diff% was 14.6 (range 0-32.5), higher in pediatric patients (mean 16.2; range 0-32.5) compared to adults (mean 12.2; range 9.7-15.4). The mean DiffAbs was 17.8 mL (range 0-42), lower in pediatric patients (mean 13.7; range 0-42) than in adults (mean 23.8; range 18-30). No significant differences were found between first- and second-day collections (Diff% p=0.22; DiffAbs p=0.49).

DiffAbs did not follow a linear trend and appeared to be influenced by the number of spillovers during the procedure.

Diff% showed moderate negative correlations with Hb (r=-0.29; p=3.48e-02), Hct (r=-0.33; p=1.47e-02), Plt count (r=-0.27; p=4.98e-02), and strong negative correlations with PW (r=-0.50; p=9.14e-05), BP (r=-0.59; p=2.36e-06) and flow rate (r=-0.50; p=1.06e-04). In contrast, DiffAbs showed moderate positive correlations with Hb (r=0.45; p=5.58e-04) and WBC (r=0.40; p=2.70e-03), and strong positive correlations with PW (r=0.77; p=4.01e-12), BP (r=0.86; p=3.50e-17), flow rate (r=0.76; p=1.87e-11) and Hct (r=0.55; p=1.85e-05).

Both collection center and patient age had a significant effect on Diff% (p= 3.37e-03 and 7.84e-04 respectively) and DiffAbs (p= 4.19e-07 and 2.11e-08 respectively), whereas sex had no significant impact (Diff% p= 0.97; DiffAbs p=0.12). Residual analysis confirmed a negative correlation between Diff% and Plt (r=-0.37; p=5.17e-03), BP (r=-0.27; p=4.25e-02), and a positive correlation between DiffAbs and WBC (r=0.32; p=1.64e-02), BP (r=0.46; p=4.34e-04), and PW (r=0.42; p=1.46e-03)—even after adjustment.

CONCLUSIONS The Spectra Optia apheresis system has been shown to overestimate the collected product volume by approximately 15%, with a mean absolute discrepancy of 18 mL. Since most of the variables influencing this measurement discrepancy are not modifiable, incorporating alternative volume assessment methods—such as weighing the collection bag—into standard operating procedures (SOPs) is advisable. This adjustment may improve the accuracy of CD34⁺ cell dose estimation and support more accurate and effective decision-making in the context of stem cell mobilization and collection strategies.

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2025
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