# Peripheral Blood as a Diagnostic Alternative to Bone Marrow in Immunophenotyping Pediatric B-Cell Acute Lymphoblastic Leukemia

## TL;DR

Peripheral blood can replace bone marrow for diagnosing pediatric B-cell leukemia when blasts are circulating, reducing the need for invasive procedures.

## Contribution

Quantifies marker-specific agreement between peripheral blood and bone marrow immunophenotyping in pediatric B-ALL.

## Key findings

- Markers like CD19+, CD10+, CD34+, and HLA-DR+ showed over 95% concordance between peripheral blood and bone marrow.
- High concordance was observed in patients with hemoglobin < 8 g/dL and those over 10 years old.
- Peripheral blood reliably reproduces most leukemic cell populations even in subgroups with lower blast levels.

## Abstract

Flow cytometric immunophenotyping is essential for the diagnosis and immunologic classification of B-cell acute lymphoblastic leukemia in children and is traditionally performed using bone marrow aspirates, an invasive procedure that may be delayed or unavailable in certain clinical contexts. However, many patients present with circulating blasts at diagnosis, raising the possibility of using peripheral blood as an alternative source for initial immunophenotypic classification. Although previous studies have shown that peripheral blood can support initial diagnostic classification, they have not determined the degree of marker-level concordance between peripheral blood and bone marrow nor the clinical conditions under which this concordance is strongest. In this study, we evaluated the immunophenotypic concordance between peripheral blood and bone marrow in 32 pediatric patients with B-cell acute lymphoblastic leukemia, using paired samples obtained at diagnosis and analyzed with a standardized panel of B-lineage and maturation markers. Accordingly, the objective of this study was to quantify marker-specific agreement between compartments and identify clinical factors associated with higher concordance. Overall concordance was moderate across all subpopulations (mean CCC ~0.63) but higher for the markers most relevant to routine diagnostic classification (e.g., CD19+, CD10+, CD34+, and HLA-DR+), several of which exceeded 95% concordance and showed minimal bias between specimens. These findings apply only to newly diagnosed B-ALL with sufficient circulating blasts, as cases with minimal residual disease, low-blast presentations, atypical immunophenotypes, or mixed-lineage leukemias were not included in this study. The greatest concordance was seen in patients with hemoglobin < 8 g/dL, in whom extensive marrow infiltration promotes blast spillover into circulation. Likewise, patients older than 10 years showed high concordance, consistent with greater leukemic burden at presentation. Even in subgroups with lower circulating blast levels, such as those with hemoglobin ≥ 8 g/dL, peripheral blood adequately reproduced most leukemic cell populations present in bone marrow. Overall, these findings indicate that the markers and subpopulations most relevant for diagnostic immunophenotyping can be reliably assessed using peripheral blood in high-burden disease settings, reducing the immediate need for invasive procedures and facilitating timely immunophenotypic classification, particularly in resource-limited environments or situations where rapid initiation of treatment is critical.