Flow Cytometric Quantitation of CD34+ Progenitors in Peripheral Blood: An Underutilized Tool in Diagnostic Evaluation of Pancytopenia

• Published in: Blood 2024-11, Vol.144, p.1316-1316
• Main Authors: Reiman, Lauren T., Vu, My H., Cotez-Bacolot, Michael, Wood, Brent L., Kovach, Alexandra E.
• Format: Article
• Language: English
• ISSN: 0006-4971
• DOI: 10.1182/blood-2024-205737

Aplastic anemia (AA) is a type of immune-mediated bone marrow (BM) failure characterized by peripheral pancytopenia and marrow hypocellularity. The disease demonstrates decreased to absent CD34+ progenitors, including hematopoietic stem cells (HSCs), due to their diminished production. In normal healthy individuals, small numbers of CD34+ progenitors are detectable in peripheral blood (PB) by flow cytometry. In patients with pancytopenia due to AA, other BM failure syndromes (genetic etiologies) and/or transient bone marrow suppression (viral or other reactive etiologies), PB CD34+ progenitors (CD34+) are expected to be decreased. Conversely, the PB CD34+ population size is expected to be maintained or increased in peripheral causes of cytopenias (destruction and/or sequestration, most immune- or infectious cases). BM CD34+ have been previously well characterized in AA (e.g. Matsui et al, Leukemia 2006), but the features - and associated clinical utility - of PB CD34+ progenitors in routine clinical flow cytometry for evaluation of pancytopenia has not been systematically studied. We hypothesized that review of a large dataset of such cases would inform evidence-based incorporation of PB CD34+ in routine clinical flow cytometry reporting. This study utilized an archival cohort of patients from Children's Hospital Los Angeles of previously healthy patients presenting between Jan 2022 and Dec 2023 with cytopenias of two or three lineages (bi- or pancytopenia) on whom a PB flow cytometry screening panel was performed. The CHLA screening panel utilizes in part a two-tube progenitor- and myeloid-focused antigen combination (M1 and M2 in Wood, Curr Protoc Cytom 2020). The flow cytometry (fcs) files were re-examined to quantify the circulating CD34+CD38+ cell population (CD34+), if present, in each of the two tubes. The average of the two tubes was expressed as a percent (%) of the average of total white blood cells (WBCs). The %CD34+ were correlated with associated clinical and laboratory characteristics including presenting symptoms, complete blood counts, findings on subsequent bone marrow biopsy if performed, and ultimate clinical diagnosis. Of the total study cohort (n=155), ultimate diagnoses to which the cytopenias were ascribed included AA (n=15, 9.7%), infection (n=44, 28.4%), other immune-mediated causes (n=41, 26.5%), metabolic disorders/nutritional deficiencies (n=10, 6.5%) non-hematologic malignancies (n=2, 1.4%) and unknown or non-specific presumed