Clinical significance of blood cell ratios in healthy and sick Leishmania infantum -seropositive dogs

The accuracy of blood cell ratios (BCRs) as cost-effective and easily accessible diagnostic and prognostic markers of inflammatory conditions has been investigated in veterinary medicine in recent years. Neutrophil-to-lymphocyte (NLR), monocyte-to-lymphocyte (MLR), and platelet-to-lymphocyte (PLR) ratios were studied in 195 dogs clinically evaluated and tested for anti- Leishmania infantum (Li) antibodies (Li -seronegative (Li −), n = 10; Li -seropositive clinically healthy (Li + ), n = 100; Li -seropositive with clinical and/or clinicopathological abnormalities (Li + ), n = 85). The Li + dogs were classified in LeishVet stages IIa/IIb (Li + ) (n = 66) and III/IV (Li + ) (n = 19). BCR relationships with LeishVet clinical stage, antibody levels, and serum protein electrophoretic fraction concentrations were investigated. Higher NLR values were found in Li +, Li + , and Li + sick dogs compared to Li − dogs (P < 0.001). Higher NLR and MLR were found in Li + (NLR, P < 0.001; MLR, P = 0.034) and Li + dogs (NLR, P < 0.001; MLR, P = 0.005) compared to Li − dogs, and in Li + dogs (NLR, P = 0.002; MLR, P < 0.001) compared to Li + . All three BCRs were higher in Li + (NLR, MLR, P < 0.001; PLR, P = 0.023) and Li + dogs (NLR P < 0.001; MLR P = 0.001; PLR, P = 0.012) compared to Li + dogs. The BCRs failed to distinguish dogs with moderate (Li + ) and severe or very severe disease (Li + ). BCRs demonstrated weak positive correlations with serum globulin fractions and antibody levels, and weak negative correlations with serum albumin level were found. Li + dogs presenting hypoalbuminemia showed higher MLR ratios (P = 0.001) than those with normal albumin values. This study shows that BCR measures provide useful information for differentiating antibody-positive healthy and sick dogs at diagnosis. Dogs with hypoalbuminemia showed higher MLR values despite monocytosis being very rare. The online version contains supplementary material available at 10.1186/s13071-024-06522-z.