Diagnostic and prognostic value of peripheral blood leucocyte ratios in sick cats

The objective of this study was to assess the diagnostic and prognostic utility of feline neutrophil-to-lymphocyte (NLR) and lymphocyte-to-monocyte ratios (LMR) in a variety of underlying diseases. Five-year medical records from cats presenting to the internal medicine unit of a veterinary teaching hospital were retrospectively reviewed. Cats were considered for inclusion based on complete medical records. ADVIA 120 was used for the complete blood counts; the NLR and LMR were calculated by dividing the absolute numbers of the respective leucocytes. Two hundred and nineteen sick and 20 healthy cats were included in the study. The median NLR and LMR were significantly (P < 0.05) elevated and decreased, respectively, in cats with infectious, neoplastic and chronic kidney diseases compared to controls. Additionally, cats with neoplasia had significantly higher median NLR compared to cats with urinary tract and gastrointestinal diseases. Non-survivors had significantly higher NLR and lower LMR compared to survivors. Both ratios had suboptimal prognostic performance for the outcome of sick cats (NLR sensitivity: 37.9%, specificity: 86.4%; LMR sensitivity: 69.0%, specificity: 61.0%). Many different disease categories were associated with increased NLR and decreased LMR compared to controls, but the overall prognostic performance of the two leucocyte ratios was suboptimal.