Pediatr Blood Cancer 2004;43:610–611

BRIEF REPORTPeripheral Blood Monocyte Count as an Aid in Optimizing

Progenitor Collection in Children

Caron Strahlendorf, MBBCh, FCP* and Grace Chan, RN, BSN

The use of hematopoietic stem cells for reconstitutionfollowing myeloablative therapy is well established inchildren with various malignant disorders. The challengeremains to accurately predict the timing and optimize theefficiency of peripheral blood stem cell harvests. To date,the quantification of circulating peripheral blood CD34þcells is the most reliable guide to predicting harvest yields[1,2]. Typically, CD34 analysis is done using a standardflow cytometer. The process involves staining, lysing, andenumeration of CD34þ cells. The turn around time is longand in some institutions, due to staffing or funding issues,flow cytometry services are not always available. Thisoften results in delays in initiating harvests with valuablenursing time wasted. Delays can cause increased patientanxiety, especially in the pediatric population. Harvestsare sometimes performed on days when the CD34þ cellcount is not optimal. More importantly, patients aresometimes put through unnecessary or inefficient harvestruns.

We wanted to investigate whether a surrogate markerexists that will aid in predicting the peripheral CD34count. The monocyte population, which reflects earlymarrow regeneration was of particular interest. Previousdata also suggested that absolute monocyte counts mayindeed be a useful indicator to predict the peak of circu-lating progenitor for harvesting autologous blood stemcells [3,4]. The question is how well does a rising trend inthe monocyte count correlate with a rising CD34 count?

We performed a retrospective analysis on all thepatients who had peripheral blood stem cell collectionsdone between 1999 and 2001. All of the patients werediagnosed with a form of malignancy and were scheduledfor peripheral blood stem cell harvest for autologous stemcell rescue following myeloablative chemotherapy. Thepriming regimens all included chemotherapy and growthfactor (G-CSF) stimulation. When the patients rebounded

from their hematological nadir, peripheralwhite blood celland differential counts were monitored daily. In addition,peripheral blood CD34 counts were monitored dailyonce the patient’s absolute neutrophil count reached1.0� 109/L. These peripheral blood samples were takendaily until the last day of harvest. CD34 values weredetermined based on the ISHAGE guidelines for CD34þcell determination using a flow cytometer (Coulter EpicsXL-MCL System II Software, Beckman Coulter, Inc.,Miami, FL). CD34þ cells were stained using a lysedno-wash whole blood method. All monoclonal (MAb)and reagents used for sample preparation were obtainedfrom the Stem-Kit CD34þ HPC Enumeration Kit(Immunotech, A Beckman-Coulter Company, Marseille,France). A total number of 40 patients contributed to140 days of evaluable data.

A peripheral blood CD34 count of 5�106/L has beenshown to be the minimum value to yield an adequateharvest [5]. On this basis, data on peripheral CD34 countswere divided into two categories: <5�106/L and �5�106/L. The corresponding peripheral monocyte countwas assigned to one of two categories: <0.7�109/L and�0.7�109/L. Normal monocyte counts on children varywith age, ranging from 0.1�109/L in an older child to0.9�109/L in an infant. We chose 0.7�109/L to representthe average age-adjusted upper limit of normal. A cross-tabulation analysis was done on the peripheral bloodCD34 counts and peripheral blood monocyte counts.

CD34 enumeration, although established asthe gold standard for timing peripheral bloodprogenitor cell harvests, is not always available.We investigated whether the peripheral bloodmonocyte population could be used to assist inpredicting the peak of circulating progenitors forharvesting autologous blood stem cells in chil-dren. A retrospective analysis was done on 140

harvests in 40 patients. Cross-tabulation analysisof peripheral blood CD34 counts and monocytecounts showed a good correlation.We concludethat in the absence of CD34 results, the mono-cyte count gives a good indication of earlymarrow regeneration and helps in predictingoptimal time for harvest. Pediatr Blood Cancer2004;43:610–611. � 2004 Wiley-Liss, Inc.

Key words: CD34; children; monocytes; peripheral blood progenitor cells

——————Department of Hematology/Oncology/Bone Marrow Transplantation,

British Columbia’s Children’s Hospital, University of British

Columbia, Vancouver, British Columbia, Canada

*Correspondence to: Caron Strahlendorf, A119–4480 Oak Street,

Vancouver, BC, V6H 3V4, Canada. 604-875-3576.

E-mail: cstrahlendorf@cw.bc.ca

Received 16 March 2004; Accepted 5 May 2004

� 2004 Wiley-Liss, Inc.DOI 10.1002/pbc.20109

A cross-tabulation analysis was also done on theperipheral blood CD34 counts and the peripheralblood total white cell count. Data on peripheral bloodCD34 counts were divided similarly with correspondingwhite cell counts assigned to one of two categories:<1.0�109/L and �1.0�109/L.

Results of the cross-tabulation analysis between theperipheral blood CD34 counts and the peripheral bloodmonocyte counts are shown in Table I.

Therewere a total of 62 samples with amonocyte countof �0.7� 109/L. Of this group, 55 correlated with aperipheral blood CD34 value of �5� 106/L with asensitivity of 88.7% and a specificity of 66.7%.

A cross-tabulation analysis was also done between theperipheral blood CD34 counts and the peripheral bloodtotal white cell counts. The results are shown in Table II.

Sixty-five percent of the samples that had a peripheralblood WBC count of �1.0� 109/L correlated with a PBCD34 value of �5� 106/L.

DISCUSSION

From our data, we conclude that a rising trend in theperipheral blood monocyte count will most of the timereflect a similar rise in the peripheral bloodCD34 count. Inthe absence of available CD34 results, themonocyte countmay give a good indication of early marrow regenerationand help in predicting optimal time for harvest. On theother hand, peripheral white blood cell counts are lessreliable in predicting time for harvest.We found that this isin agreement with previous studies [6,7].

In our centre, we are now monitoring peripheral bloodmonocyte counts in addition to peripheral blood CD34counts for all our stem cell harvests, especially on week-ends when CD34 analysis is not available to us. In severalinstances, this has enabled us to minimize delay incommencing harvests while awaiting CD34 results. Theoverall outcome is more optimal patient care and savingsin time and costs.Wewill continue to collect data to assessthe accuracy of using the peripheral bloodmonocyte countas a tool to assist in planning stem cell harvests.

REFERENCES

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5. Strahlendorf C, Nelson M, Chan G, et al. Peripheral blood count to

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TABLE I. Cross-Tabulation Analysis of Peripheral Blood CD34Counts and Peripheral Blood Monocyte Counts

Peripheral blood

monocyte count

<0.7�109/L

Peripheral blood

monocyte count

�0.7�109/L

Peripheral blood

CD34 <5�109/L n 52 7

% 66.7 11.3

Peripheral blood

CD34 �5�106/L n 26 55

% 33.3 88.7

TABLE II. Cross-Tabulation Analysis of Peripheral Blood CD34Counts and Peripheral Blood Total White Blood Cell Count

Peripheral blood

total WBC count

<1.0�109/L

Peripheral blood

total WBC count

�1.0�109/L

Peripheral blood

CD34 <5�106/L n 18 41

% 78.3 35.0

Peripheral blood

CD34 �5�106/L n 5 76

% 21.7 65.0

Peripheral Blood Monocyte 611