Diagnostic Evaluation of the Sysmex <scp>XN</scp> ‐ <scp>1000V</scp> Lymphocyte Fluorescence for Differentiating Canine Nodal Large B‐Cell and T‐Cell Lymphoma

Canine lymphoma is a common haematopoietic neoplasm. Immunophenotype is a major prognostic factor and may influence treatment recommendations. This study assessed the diagnostic performance of the Sysmex XN-1000V white blood cell differential (WDF) scattergram to differentiate canine nodal large B-cell and T-cell lymphoma, using the percentage of highly fluorescent cells (%HFC) and visual WDF scattergram evaluation. A retrospective study was conducted on data from cases of cytologically diagnosed canine large cell lymphoma. Cases had concurrent lymph node aspirate cell suspensions in saline that were analysed using the Sysmex XN-1000V and multiparametric flow cytometry (FC) for lymphoma classification as B or T-cell. Large B-cell lymphomas (n = 86) showed significantly higher %HFC compared to large T-cell lymphomas (n = 17), with a median (IQR) of 50% (36-84) and 9.7% (3.9-19), respectively. The ROC analysis showed an AUC of 0.93, with an optimal cutoff of < 24.15 %HFC for identifying T-cell lymphoma, achieving 88.24% sensitivity, 87.21% specificity, 57.69% PPV and 97.40% NPV. The following data is expressed as 'overall-percentage-agreement (kappa value)'. Using the previous cutoff, the agreement between the %HFC classification and FC was 88.24% (κ = 0.76). Regarding the WDF scattergram evaluation, the intra- and inter-observer agreement were 86.27% (κ = 0.71) and 67.65% (κ = 0.55), respectively. Agreement between the WDF scattergram evaluation and FC was 77.45% (κ = 0.55), and improved to 90.63% (κ = 0.74) when just the confident cases were used. In conclusion, a preliminary assessment of the phenotype of canine nodal large cell lymphoma can be made using either the visual inspection of the WDF scattergram or the %HFC. This could serve as a cost-effective, fast screening tool while awaiting definitive flow cytometry results.