Difference from Normal (∆N:) Flow Cytometry is typically the first test performed to determine specimen composition. Through the ∆N: approach pioneered by Dr. Michael Loken, Founder and President of Hematologics, we can identify both the lineage and maturational stage of each cell population. Hematopoiesis is a dynamic process where cell maturation must be followed from stem cell to maturity, and traditional multiparameter flow cytometry provides only a static result at an individual point in this process. Our approach focuses on patterns to identify the normal populations first. This provides the normal for the ∆N: comparisons and quality control for each tube in the assay. Using this approach, we can confidently identify residual AML and ALL cells at levels down to 0.02%, even without a diagnostic specimen. Similarly, we can detect phenotypic abnormalities in patients with unexplained cytopenias (i.e., myelodysplastic syndromes (MDS)). Hematologics is a founding member of the European Leukemia Network MDS Flow Cytometry Working Group.
∆N: Flow Cytometry measures the intensity of gene product expression, as opposed to measuring the frequency by counting positive and negative populations as other laboratories do. Four color, six-dimensional analysis is performed eliminating the need for large panels. As laboratories continue to add more colors, they limit themselves to two-dimensional analysis losing the relationship between markers and overall assay sensitivity. It should be noted that the ∆N: assay is the only MRD assay that can be used without a diagnostic specimen; although one greatly helps.
The abnormal cell populations in hematopoietic malignancies (including but not limited to acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia, myelodysplasia, chronic lymphocytic leukemia, hairy cell leukemia, non-Hodgkin B and T cell lymphoma, plasma cell myeloma) and some instances of non-hematopoietic malignancies can be identified in peripheral blood and bone marrow aspirate specimens using ∆N: Flow Cytometry. The diagnostic and prognostic information obtained by flow cytometry supplements clinical, morphological, and cytogenetic parameters.
Cells for flow cytometric analysis can also be obtained from lymph node biopsies, fine needle aspirates of lymph nodes or tissue masses, or from body fluids (e.g., CSF or pleural effusions). Detection of neoplastic cells of B-lineage origin is based on ∆N: in conjunction with the cellular expression (surface or cytoplasmic) of immunoglobulin restricted to either kappa or lambda light chain. T-lineage neoplasms are identified by the aberrant expression of T-lymphoid antigens.
It is crucial to distinguish viable from dead cells in these specimens since poor cell viability may give false positive or uninterpretable results. We use ∆N: in combination with a viability dye to assess only the intact live cells to accurately phenotype the cells in these tissues.
The combination of cell size by light scatter and immunophenotype correlates well with established histological criteria for non-Hodgkin lymphoma while providing sensitive detection techniques for minimal residual disease.