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Subject: White Blood Cell Counts and Differentials
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WBC counts refer to numerical reporting of the total number of WBCs as well as to describing and classifying the white cell components: neutrophils (which include bands), lymphocytes, monocytes, eosinophils, and basophils (Table 16.88).
Normal range (adults): 4.3–10.3 × 103 cells/μL. Different values are reported for infants and children, separated by age groups. Automated counters report results in percentages or as absolute counts of each WBC population. The absolute differential counts are considered more relevant in evaluating WBC abnormalities.
Most automated WBC counters separate the white cells into five categories. Immature white cells are flagged as abnormal, requiring direct examination of the peripheral blood smears. Recent machines do a six-part differential, the sixth parameter being “immature fraction.”
Abnormalities are discussed separately for each population (see Leukocytosis and Leukopenia and Leukemoid).
Poorly prepared stains (mostly the manual ones) may corrupt the ability of the technician to report accurate differentials.
Because in most laboratories the technician examines only 100 randomly selected cells, there is an inherent bias in the report, and rare, but important, abnormal WBCs may be missed, especially in leukopenic conditions. With the recent introduction of automated equipment for reporting differential counts this bias is minimized.