_1793849865 20261105033745000 Rovedar Daryoushbabazadeh@gmail.com Rovedar Small Animal Advances Small Anim. Adv. 2821-2363 10 03 2026 5 3 Ramtin Ghorban Pour https://orcid.org/0009-0003-8242-7517 Ali Heydari https://orcid.org/0009-0003-4806-082X Ghazaleh Kompani https://orcid.org/0009-0008-9860-0050 Sara Sadat Tavakoli https://orcid.org/0009-0007-5499-2817 Hossein Zaree https://orcid.org/0009-0008-5832-4792 Ali Jebeli Eshrat Abadi https://orcid.org/0009-0004-3059-5188 Parsa Jahani https://orcid.org/0000-0001-7073-2205 Narges Anari https://orcid.org/0009-0008-0381-0371 Introduction: Acute gastroenteritis (AGE) in dogs ranges from mild to severe, requiring supportive care. Serum lactate reflects tissue perfusion and metabolic status, while the neutrophil-to-lymphocyte ratio (NLR) marks systemic inflammation. The present study aimed to assess the value of serum lactate and NLR as early predictors of disease severity in dogs with AGE. Materials and methods: In this prospective clinical study, 72 dogs (39 males and 33 females) with AGE and a mean age of 4.5 years were included. Clinical severity was assessed based on predefined clinical criteria, including degree of dehydration, frequency of vomiting and diarrhea, body temperature, heart rate, mental status, and need for hospitalization or intensive supportive treatment using intravenous fluid therapy and antiemetic administration. Blood samples were collected to determine serum lactate concentration and complete blood count before any treatment, including intravenous fluid therapy and antiemetic administration. The NLR was calculated from absolute neutrophil and lymphocyte counts. Correlation and regression analyses were performed to assess how these biomarkers were associated with clinical severity. Receiver operating characteristic (ROC) analysis assessed the ability of NLR to distinguish severe disease from mild-to-moderate disease.Results: Serum lactate concentrations and NLR were higher in dogs with severe AGE compared with dogs with mild-to-moderate gastroenteritis. Serum lactate concentrations and NLR revealed significant positive correlations with clinical severity scores. Higher lactate concentrations and NLR were associated with prolonged hospitalization and the need for intensive supportive treatment. In multivariate analysis, serum lactate and NLR remained independently associated with gastroenteritis. Based on ROC analysis, combining lactate and NLR provided superior discrimination compared to using each biomarker individually; thus, the combination offered enhanced discriminative ability. 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