How should chronic hepatitis in dogs be diagnosed and differentiated from other hepatic diseases?

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Chronic hepatitis (CH) in dogs is definitively diagnosed by hepatic biopsy, which remains the gold standard, after ruling out infectious, toxic, copper-associated, and neoplastic causes through a structured pre-biopsy workup. 15 The minimum diagnostic database before biopsy includes serum alanine aminotransferase (ALT) activity, full biochemistry panel, urinalysis, abdominal imaging, and infectious disease screening. CH is defined by persistent ALT elevation greater than 2 times the upper limit of normal accompanied by histopathological changes: hepatocellular apoptosis or necrosis, a variable mononuclear or mixed inflammatory cell infiltrate, regeneration, and fibrosis. 1810 Hepatitis of 4 to 6 months' duration meets the threshold for classification as chronic. 3 Infectious causes must be excluded before attributing CH to immune-mediated or idiopathic etiologies. Leptospira interrogans serovars Icterohaemorrhagiae and Pomona and chronic infections with L. interrogans serotype Grippotyphosa and L. kirschneri serotype Grippotyphosa are associated with hepatic disease in dogs, presenting with vacillating to markedly increased liver enzyme activity with or without hyperbilirubinemia. 11 Antinuclear antibody testing, endemic infectious disease titers or antigen tests, and a thorough drug, toxin, dietary, environmental, and family history are required before a case can be classified as idiopathic. 7 Copper-associated hepatitis is the most important specific etiology to exclude and requires both quantitative hepatic copper determination and qualitative copper staining on biopsy. Labrador Retrievers are predisposed to copper-associated hepatitis through mutations in the copper transporter genes ATP7B and ATP7A, and dietary copper intake contributes to disease progression in this breed. 12 Lobe-to-lobe heterogeneity in hepatic copper deposition and loss of detectable lobular copper distribution in late-stage disease can complicate exclusion of copper toxicosis even with bio