Validation of the Sysmex XT-2000iV hematology system for dogs, cats, and horses. II. Differential leukocyte counts

The Sysmex XT-2000iV is a laser-based, flow cytometric hematology system that stains nucleic acids in leukocytes with a fluorescent dye. A 4-part differential is obtained using side fluorescence light and laser side scatter.

The purpose of this study was to validate the Sysmex XT-2000iV for determining differential leukocyte counts in blood from ill dogs, cats, and horses.

Blood samples from diseased animals (133 dogs, 65 cats, and 73 horses) were analyzed with the Sysmex XT-2000iV (Auto-diff) and the CELL-DYN 3500. Manual differentials were obtained by counting 100 leukocytes in Wright-stained blood smears.

Leukocyte populations in the Sysmex DIFF scattergram were usually well separated in equine samples, but were not as well separated in canine and feline samples. Correlation among the Sysmex XT-2000iV, CELL-DYN 3500, and manual counts was excellent for neutrophil counts (r >or=.97) and good for lymphocyte counts (r >or=.87) for all three species. Systematic differences between the 3 methods were seen for lymphocyte and monocyte counts. The Sysmex reported incomplete differential counts on 18% of feline, 13% of canine, and 3% of equine samples, often when a marked left shift (>10% bands) and/or toxic neutrophils were present. Eosinophils were readily identified in cytograms from all 3 species. Neither the Sysmex nor the CELL-DYN detected basophils in the 7 dogs and 5 cats with basophilia.

The Sysmex XT-2000iV automated differential leukocyte count performed well with most samples from diseased dogs, cats, and horses. Basophils were not detected. Immature neutrophils or prominent toxic changes often induced errors in samples from cats and dogs.