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⁺_healthy), n = 100; Li-seropositive with clinical and/or clinicopathological abnormalities (Li⁺_sick), n = 85). The Li⁺_sick dogs were classified in LeishVet stages IIa/IIb (Li⁺_IIa/IIb) (n = 66) and III/IV (Li⁺_III/IV) (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⁺_healthy, and Li⁺_IIa/IIb sick dogs compared to Li⁻ dogs (P < 0.001). Higher NLR and MLR were found in Li⁺_sick (NLR, P < 0.001; MLR, P = 0.034) and Li⁺_III/IV dogs (NLR, P < 0.001; MLR, P = 0.005) compared to Li⁻ dogs, and in Li⁺_III/IV dogs (NLR, P = 0.002; MLR, P < 0.001) compared to Li⁺_healthy. All three BCRs were higher in Li⁺_sick (NLR, MLR, P < 0.001; PLR, P = 0.023) and Li⁺_IIa/IIb dogs (NLR P < 0.001; MLR P = 0.001; PLR, P = 0.012) compared to Li⁺_healthy dogs. The BCRs failed to distinguish dogs with moderate (Li⁺_IIa/IIb) and severe or very severe disease (Li⁺_III/IV). BCRs demonstrated weak positive correlations with serum globulin fractions and antibody levels, and weak negative correlations with serum albumin level were found. Li⁺_sick 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.