While liver disease in people is very well classified, the hepatic pathology in dogs lacks definitive classification. This impedes our ability to assess the clinical and pathological significance of canine liver disease.

The term "chronic active hepatitis" may be inappropriate in the dog. Chronic progressive hepatitis is the preferred term. True chronic progressive hepatitis is an uncommon disease in dogs, except in Labrador and Golden retrievers.

Pathology is often unevenly distributed throughout the liver and biopsy findings are dependent on the site and type of biopsy:

• True-Cut Type Needle Biopsy. Use a 16-18 gauge needle. Two pieces of representative tissue, ~½–¾ inch long should suffice. Selecting the tissue site is critically important and can be assisted by ultrasound guidance. Focal disease may be easily missed with needle biopsy.
• Wedge Biopsy. Acceptable technique if a large enough wedge of liver is excised. Care is needed with interpretation of pathology in the subcapsular parenchyma. Liver margins can become damaged with aging from episodes of anemia, hypotension, shock, small infarcts, etc., which lead to fibrous tissue deposition. These changes are most likely to be seen in older patients and can be mistakenly interpreted as chronic hepatitis or cirrhosis, especially if only a small piece of liver is biopsied.
• Fine Needle Aspirate. Reasonable technique for first assessment. If cytology findings don’t match clinical suspicions, then true-cut type or wedge biopsy may be required. FNA cytology can determine whether inflammatory cells are present, as can occur with inflammatory bowel disease (IBD), cancer, pancreatitis, and other systemic inflammatory diseases (reactive hepatopathy), leptospirosis, ehrlichiosis, or chronic hepatitis. FNA cytology does not enable a specific diagnosis of chronic, progressive hepatitis. In cats with inflammatory liver disease, the presence of neutrophils (alone or together with lymphocytes and plasma cells) suggests cholangiohepatitis, either due to ascending bacterial infection or secondary to IBD/pancreatitis. If only lymphoid cells are present, lymphoma or lymphocytic portal hepatitis (which has not been associated with IBD/pancreatitis) is more likely.