The Canine Leishmaniosis Proteinogram: A Reference Serum Electrophoretic Atlas of 5544 Dogs over 18 Years

Abstract

Serum protein capillary electrophoresis can characterise dysproteinaemia in dogs tested for canine leishmaniosis (CanL) as an integrated clinicopathological phenotype of humoral immune activation. This retrospective laboratory-based study evaluated serum protein electrophoretic patterns in 5544 dogs tested for CanL in Portugal between 2009 and 2026. Anti-Leishmania antibody results were classified into five ordered categories: negative, inconclusive, low positive, positive/high positive and very high positive. Total protein, albumin, alpha-1, alpha-2, beta and gamma fractions, albumin-to-globulin and albumin-to-gamma-globulin ratios were analysed. A separately defined reference subpopulation of 254 clinically healthy seronegative dogs aged ≥ 1 to <4 years was used to establish study-specific non-parametric 95% reference intervals. After excluding inconclusive results, binary analysis included 2454 seronegative and 2910 seropositive dogs. Seropositive dogs had higher median gamma globulins than seronegative dogs (1.5 vs. 0.8 g/dL; p < 0.001), with lower albumin-to-globulin (0.7 vs. 1.0; p < 0.001) and albumin-to-gamma-globulin ratios (1.9 vs. 4.2; p < 0.001). Across the ordinal serological scale, gamma globulins increased from 0.8 to 2.1 g/dL (p < 0.001), whereas the albumin-to-gamma-globulin ratio decreased from 4.2 to 1.2. Gamma globulins showed the strongest ordinal association (ρ = 0.522; p < 0.001) and moderate single-marker discrimination of seropositivity (area under the receiver operating characteristic curve = 0.768; 95% confidence interval: 0.755–0.780). These findings define the CanL proteinogram as a progressive, quantifiable immunopathological phenotype, dominated by gamma-region expansion and reciprocal albumin decline, supporting serum protein electrophoresis as a reference tool for interpretation and monitoring.