Serum Alkaline Phosphatase Level On Day 4 Of G-CSF Administration Could Be a Simple Yet Practical Surrogate Marker For CD34 Mobilization and Collection
Authors: Zakharia Yousef , Kota Vamsi , Mansour Joshua , Prabhakar Radhika , Lan Ling , Awan Farrukh T , Jillella Anand 
Published: October 2019

Introduction
Granulocyte colony stimulating factor (G-CSF) mobilized peripheral blood stem cells (PBSCs) have become the primary source of stem cells in the majority of allogeneic stem cell transplantations, mainly because of ease of collection and rapid hematopoietic reconstitution. G-CSF for 4 days is the preferred stem cell mobilization method for normal donors. Peripheral blood CD34+ cell count on day 4 of G-CSF is used as a guide to initiate apheresis and PBSC collection. The actual cutoff for PBSC collection varies by institutional preferences. At our center, we collect PBSCs when the CD34+ cell count is greater than 15/ml. Since the turnaround time for CD34 count is about 3 hours; there is a delay in the start of apheresis which extends the PBSC collection to a second day. A reliable and faster method which estimates CD34+ cell count will enable us to avoid delays in collection to the next day. We report the data from our center on the utility of serum alkaline phosphatase (ALK.ph) level as a surrogate marker for the adequacy of peripheral blood CD 34+ cell count suitable for stem cell collection.

Methods
A retrospective chart review on normal PBSC donors for allogeneic stem cell transplant between January 1, 2009 and March 31, 2013, was performed after obtaining IRB approval. Data was collected at baseline to include sex, age, BMI, WBC, ALK.ph and day 4 ALK.ph, WBC and CD34 count.

Results
51 PBSC donors were evaluated, 2 patients were excluded for baseline ALK.ph> 200 which was due to undetermined causes. None of these donors had a history of hematologic malignancies or underwent previous apheresis procedures. Of the 49 evaluable patients (23 were males); the median age was 53 years (range 11-72), and the median body mass index (BMI) was 29.1 (range 14-78). Median baseline ALK.ph was 72 (range 42-150), the median day 4 ALk.ph was 164 (54-279). The median CD34 count on first day of collection was 47 (5-218) and there were no mobilization failures.
A positive correlation was observed between CD34 count and increase in ALK ph levels 0.4171 (p=0.002). For every one unit/ liter increase in alkaline phosphatase there is 0.48 times (95% CI 0.17-0.78) increase in CD34 count.
On univariate regression analysis, the factors that were correlated with CD34+ cell counts were day 4 alkaline phosphatase (p=0.015), day 4 WBC count (p<0.001) and change in alkaline phosphatase as compared to baseline (p=0.002). However, on multivariate robust regression analysis, factors that were correlated with CD34 counts were gender (p=0.04), day 4 WBC count (p<0.001) and baseline alkaline phosphatase (p=0.027).

Conclusion
Our analysis suggests a potential utility of the change in serum alkaline phosphatase level at day 4 after GCSF in predicting peripheral blood CD34+ cell count. Further studies are underway to utilize this information as part of an algorithm to improve efficiency and prevent delays in normal donors undergoing PBSC mobilization and harvesting.

Disclosures:
No relevant conflicts of interest to declare.