Editor: Frederick L. Kiechle, MD, PhD
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Q. When performing body fluid cell counts, we report total nucleated cells and RBCs. What cell categories should we report on the corresponding differential? Can we group together monocytes, macrophages, and mesothelial cells since it is difficult to distinguish reactive mesothelial cells from monocytes and macrophages? If so, what category name should be applied? Should we report mesothelial cells as a comment or include them in the differential?
A. September 2024—It is tempting to group mesothelial cells and other cells that line body cavities and organs with monocytes and macrophages given their morphological overlap at times, especially under reactive conditions. However, clinically meaningful information may be missed if these cell types are grouped together. For example, an abundance of macrophages may suggest an infectious or other reactive process, and this could be overlooked if the macrophages are grouped with mesothelial cells.
Although it may not be possible to identify each cell with absolute certainty, the overall characteristics of the cell population—that is, cytologic similarities to other cells in the sample—can often distinguish mesothelial cells from monocytes or macrophages in most settings. In morphologically challenging cases, a narrative comment may be included with the differential if technologists and pathologists cannot reach a consensus after examining a sufficient number of cells.
The differential for body fluid specimens should include all common cell types present on the cytospin slide(s). The percentage of each cell type, including for hematopoietic and non-hematopoietic cells, should be calculated from a denominator since the differential can include cells lining a body cavity, metastatic tumor cells, and hematopoietic cells. In the past, some laboratories reported only hematopoietic cells (i.e. a total white blood cell count) instead of a total nucleated cell count. Because reporting the white blood cell count can be misleading, particularly for samples containing numerous non-hematopoietic tumor cells and/or lining cells, the CAP added checklist requirement HEM.35650 Body Fluid Result Reporting of Nucleated Cells in 2021.
The laboratory director ultimately is responsible for determining which specific cell types to enumerate and which nomenclature suits local practice needs.
Bourner G, De la Salle B, George T, et al.; International Committee for Standardization in Hematology. ICSH guidelines for the verification and performance of automated cell counters for body fluids. Int J Lab Hematol. 2014;36(6):598–612.
Clinical and Laboratory Standards Institute. H56-A: Body Fluid Analysis for Cellular Composition; Approved Guideline; 2006.
College of American Pathologists. HEM.35650 Body fluid result reporting of nucleated cells. In: Hematology and coagulation checklist. Aug. 24, 2023.
Kjeldsberg CR, Knight JA. Body Fluids: Laboratory Examination of Amniotic, Cerebrospinal, Seminal, Serous & Synovial Fluids. American Society of Clinical Pathologists; 1993.
Alexandra E. Kovach, MD
Director, Hematopathology
Medical Director, Hematology and Bone Marrow Laboratories
Department of Pathology and Laboratory Medicine
Children’s Hospital Los Angeles
Associate Professor of Clinical Pathology
Keck School of Medicine
University of Southern California
Los Angeles, Calif.
Member, CAP Hematology/Clinical Microscopy Committee
Q. Are nonlaboratory personnel who perform point-of-care testing required to be tested for visual color discrimination? Or is it sufficient that personnel pass a functional assessment during their competency evaluation to evaluate their ability to provide an accurate result on tests that require interpreting colors?
A. All personnel performing testing or other laboratory-related tasks that require color discrimination need to be evaluated for difficulty with color discrimination. CAP checklist requirement GEN.55400 Visual Color Discrimination allows laboratories to define how personnel are evaluated for the ability to discriminate colored items pertinent to their jobs. Many facilities use a standardized method for screening (e.g. a pseudoisochromatic color vision test), but a documented functional assessment for discriminating colored items that pertain to a person’s job duties may also be used. A general competency assessment alone does not satisfy the checklist requirement. Each facility should have defined policies on how to evaluate personnel for their ability to discriminate color and what documentation is required.
Shelley Martire, MLS(ASCP)CM
Senior Technical Specialist
CAP Laboratory Accreditation Program
College of American Pathologists
Northfield, Ill.