Background: The LaserCyte hematology analyzer (IDEXX Laboratories, Chalfont St. Peter, Bucks, UK) is the first in-house laser-based single channel flow cytometer designed specifically for veterinary practice. The instrument provides a full hematologic analysis including a 5-part WBC differential (LC-diff%). We are unaware of published studies comparing LC-diff% results to those determined by other methods used in practice.
Objective: To compare LC-diff% results to those obtained by a manual differential cell count (M-diff%).
Methods: Eighty-six venous blood samples from 44 dogs and 42 cats were collected into EDTA tubes at the Forest Veterinary Centre (Epping, UK). Samples were analyzed using the LaserCyte within 1 hour of collection. Unstained blood smears were then posted to Langford Veterinary Diagnostics, University of Bristol, and stained with modified Wright's stain. One hundred-cell manual differential counts were performed by 2 technicians and the mean percentage was calculated for each cell type. Data (LC-diff% vs M-diff%) were analyzed using Wilcoxon signed rank tests, Deming regression, and Bland-Altman difference plots.
Results: Significant differences between methods were found for neutrophil and monocyte percentages in samples from dogs and cats and for eosinophil percentage in samples from cats. Correlations (r) (canine/feline) were .55/.72 for neutrophils, .76/.69 for lymphocytes, .05/.29 for monocytes and .60/.82 for eosinophils. Agreement between LC-diff% and Mdiff% results was poor in samples from both species. Bland-Altman plots revealed outliers in samples with atypical WBCs (1 cat), leukocytosis (2 dogs, 9 cats), and leukopenia (16 dogs, 11 cats). The LaserCyte generated error flags in 28 of 86 (32.6%) samples, included 7 with leukopenia, 8 with lymphopenia, 7 with leukocytosis, 1 with anemia, and 1 with erythrocytosis. When results from these 28 samples were excluded, correlations from the remaining nonflagged results (canine/feline) were .63/.65 for neutrophils, .67/.65 for lymphocytes, .11/.33 for monocytes, and .63/.82 for eosinophils.
Conclusion: Although use of a 100-cell (vs 200-cell) M-diff% may be a limitation of our study, good correlation between WBC differentials obtained using the LaserCyte and the manual method was achieved only for feline eosinophils.