Evaluation of platelet surface-associated immunoglobulin positivity and its association with hematologic findings and vector-borne pathogens in thrombocytopenic dogs

BACKGROUND: Platelet surface-associated immunoglobulin (PSAIG) occurs in thrombocytopenic dogs with vector-borne diseases and immune thrombocytopenia (ITP) and may be associated with thrombocytopenia severity and inflammatory markers, including neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios (NLR, PLR). HYPOTHESIS/OBJECTIVES: Assess associations between PSAIG positivity, hematologic parameters, thrombocytopenia severity, and vector-borne status in thrombocytopenic dogs. ANIMALS: Sixty-nine client-owned thrombocytopenic dogs (<200 × 103/μL) were enrolled between June 2022 and June 2023. METHODS: Dogs were prospectively enrolled. Platelet surface-associated immunoglobulin was measured using flow cytometry. Vector-borne pathogens were assessed by serology (Ehrlichia spp., Anaplasma spp., Borrelia burgdorferi, Dirofilaria immitis) and PCR for Ehrlichia canis. Hematologic parameters were compared between PSAIG groups (Mann-Whitney U), and associations tested by univariable logistic regression. RESULTS: Dogs positive for PSAIG (n = 16) had lower median automated platelet counts (16.5 × 103/μL; interquartile range [IQR]: 8.25-40.75) than PSAIG-negative dogs (n = 53; 64 × 103/μL; IQR: 25.0-92.5; P = .001), with similarly lower manual platelet counts (48 × 103/μL; IQR: 20-86 vs 96 × 103/μL; IQR: 55-138; P = .01) and automated PLR (7.14; IQR: 3.30-15.28 vs 21.82; IQR: 9.42-38.99; P = .01). In logistic regression, PSAIG positivity was associated with lower platelet counts and automated PLR, E. canis PCR positivity, and Anaplasma seropositivity, with the strongest association for concurrent E. canis PCR and Anaplasma seropositivity (odds ratio [OR]; 15.3; 95% confidence interval [CI]: 2.69-86.99; P = .002). CONCLUSIONS AND CLINICAL IMPORTANCE: Lower platelet counts and automated PLR were associated with PSAIG positivity in thrombocytopenic dogs. Associations between PSAIG, E. canis infection, and co-exposure to Anaplasma spp. support immune-mediated platelet destruction in infected dogs.