Is the Hemocytometer Obsolete for Body Fluid Cell Counting?

Abstract

Automated body fluid (BF) cell counts performed on hematology analyzers have been steadily replacing manual hemocytometer (counting chamber) cell counts in clinical laboratories. Hematology analyzers with dedicated BF modes are capable of producing an RBC count, total nucleated cell (TNC) count, WBC count, and a limited WBC differential count. Distinguishing TNCs from WBCs is particularly useful for serous fluids, where body cavity lining cells may be present in significant numbers and can interfere with the accuracy of manual WBC counts if they are not excluded. Although lining cells rarely interfere with WBC counts in cerebrospinal fluid (CSF), the extremely low CSF WBC concentrations relative to blood have limited the use of automated hematology analyzers for CSF cell counts. Achieving the accuracy and precision required to reliably distinguish pathologic CSF specimens from normal samples has posed a challenge to automated hematology analyzer manufacturers. In this issue, Fleming et al1 present an evaluation of a new high-sensitivity analysis (hsA) BF mode on the Sysmex XN hematology analyzer (Sysmex, Kobe, Japan) for CSF cell counts. The hsA BF mode is not yet commercially available but can be accessed for research purposes on the XN analyzers. Their results suggest that Sysmex has met the challenge of automated enumeration of WBCs and RBCs in CSF samples. The limit of quantitation (LoQ) expresses the precision (functional sensitivity) of the analyzer and is useful for comparing the accuracy of different analyzers for low cell counts, such as exist in CSF.2 These investigators defined LoQ as the lowest cell count that can be obtained … Corresponding author: Linda M. Sandhaus, MD, University Hospitals Case Medical Center, 11100 Euclid Ave, Cleveland, OH 44106; Linda.Sandhaus{at}UHhospitals.org.