Extended leukocyte parameters for hematology analyzers.

Newly introduced, extended leukocyte parameters on laser-based hematology analyzers permit normal samples to be readily identified allowing these samples to be excluded from manual analysis. This enables more hematology laboratory resources to be focused on abnormal specimens. A new reagent that lyses erythrocytes while leaving the optical properties of the leukocytes unaltered is used. A special optical bench measures both narrow-angle forward light scatter (an indicator of cell size) and wide-angle light scatter (an indicator of cell granularity). The two scatter measurements are combined to produce a histogram in which lymphocytes, monocytes, and granulocytes are clearly delineated. A microprocessor detects the separation between histogram peaks, sets the proper thresholds, produces the three-part count, and indicates abnormal samples on the basis of histogram peak position, shape, and resolution. In a clinical study correlations between instrument counts and manual leukocyte differentials were very good. The potential for reducing the number of manual differentials of normal samples is significant.