A system for conducting a white blood cell differential analysis on a sample of whole blood, the system comprising: (a) a hematology analyzer, the hematology analyzer comprising: an excitation source positioned to excite particles within the blood sample; a plurality of detectors including an axial light loss detector positioned to measure axial light loss from the excited blood sample, an intermediate angle scatter detector positioned to measure intermediate angle scatters from the excited blood sample, a polarized side scatter detector positioned to measure large angle polarized side scatters from the excited blood sample, a depolarized side scatter detector positioned to measure large angle depolarized side scatter from the excited blood sample, and a fluorescence detector positioned to measure fluorescence emitted from the excited blood sample; and a processor configured to: receive the measurements of axial light loss, intermediate angle scatters, large angle polarized side scatters, large angle depolarized side scatters, and fluorescence from the plurality of detectors, and perform a WBC differential analysis of the blood sample, based on all five measurements, for particles that emit fluorescence above a fluorescence threshold; and (b) a reagent for analyzing WBCs in the sample, the reagent comprising: a membrane-permeable fluorescent dye; a WBC protecting agent; and an osmolality adjustment component; wherein the concentration of the membrane-permeable fluorescent dye is sufficient to facilitate identification of one or more cells in the sample that contain a nucleus using the hematology analyzer; and wherein the concentration of the osmolality adjustment component is sufficient to facilitate identification of a plurality of subpopulations of WBCs in the sample using the hematology analyzer, characterized in that the concentration of the osmolality adjustment component ranges from 0.1% to 0.5% and that the osmolality adjustment component comprises ammonium chloride and sodium chloride, in order to separate a plurality of WBC subpopulations from one another when analyzed with the hematology analyzer. (a) a hematology analyzer, the hematology analyzer comprising: an excitation source positioned to excite particles within the blood sample; a plurality of detectors including an axial light loss detector positioned to measure axial light loss from the excited blood sample, an intermediate angle scatter detector positioned to measure intermediate angle scatters from the excited blood sample, a polarized side scatter detector positioned to measure large angle polarized side scatters from the excited blood sample, a depolarized side scatter detector positioned to measure large angle depolarized side scatter from the excited blood sample, and a fluorescence detector positioned to measure fluorescence emitted from the excited blood sample; and a processor configured to: receive the measurements of axial light loss, intermediate angle scatters, large angle polarized side scatters, large angle depolarized side scatters, and fluorescence from the plurality of detectors, and perform a WBC differential analysis of the blood sample, based on all five measurements, for particles that emit fluorescence above a fluorescence threshold; and an excitation source positioned to excite particles within the blood sample; a plurality of detectors including an axial light loss detector positioned to measure axial light loss from the excited blood sample, an intermediate angle scatter detector positioned to measure intermediate angle scatters from the excited blood sample, a polarized side scatter detector positioned to measure large angle polarized side scatters from the excited blood sample, a depolarized side scatter detector positioned to measure large angle depolarized side scatter from the excited blood sample, and a fluorescence detector positioned to measure fluorescence emitted from the excited blood sample; and a processor configured to: receive the measurements of axial light loss, intermediate angle scatters, large angle polarized side scatters, large angle depolarized side scatters, and fluorescence from the plurality of detectors, and perform a WBC differential analysis of the blood sample, based on all five measurements, for particles that emit fluorescence above a fluorescence threshold; and receive the measurements of axial light loss, intermediate angle scatters, large angle polarized side scatters, large angle depolarized side scatters, and fluorescence from the plurality of detectors, and perform a WBC differential analysis of the blood sample, based on all five measurements, for particles that emit fluorescence above a fluorescence threshold; and (b) a reagent for analyzing WBCs in the sample, the reagent comprising: a membrane-permeable fluorescent dye; a WBC protecting agent; and an osmolality adjustment component; a membrane-permeable fluorescent dye; a WBC protecting agent; and an osmolality adjustment component;