Hepatic needle true-cut biopsies (especially 18-gauge) collected under ultrasonographic guidance may yield samples that are too small and fragmented for accurate diagnosis because of a lack representative acinar units (at least 15 portal triads should be sampled). Furthermore, needle biopsies are usually only collected from the more safely sampled left-sided lobes which may miss lesions differentially affecting liver lobes (eg cholangiohepatitis in cats). Blind-needle biopsies done without ultrasonographic guidance are hazardous and ill advised. In animals with suspected hepatic hilar or mesenteric lymphadeno-megaly; involvement of the common bile duct, gallbladder, intestines (eg, inflammatory bowel disease, infiltrative disease), or pancreas; or multiple organ abnormalities, an exploratory laparotomy is most appropriate. When possible, wedge biopsies or laparoscopic cup forcep biopsies are preferred methods because samples of adequate size can be easily and safely acquired from multiple liver lobes, ensuring accurate disease representation. Laparoscopic methods are not recommended when disease of the common bile duct or gallbladder may necessitate a decompressive biliary procedure, cholecystectomy, or cholestotomy. Liver biopsy should always be done even if an obvious biliary abnormality is the predominate disease process because an parenchymal disorder may be the primary disease process. It is also important to biopsy grossly normal liver when focal lesions are identified to determine if an underlying liver disease exists separate from the identified focal abnormality.

Routine biopsy evaluation should include examination of a cytologic imprint, Gram stain (if suppurative or pyogranulomatous inflammation is cytologically detected), histologic staining, aerobic and anaerobic bacterial cultures of liver and bile, and quantification of hepatic copper, iron, and zinc concentrations. A tissue sample should also be reserved for other special case-specific studies if needed later.

Before biopsy, bleeding tendencies should be evaluated by careful review of the history, physical examination, blood smear (to confirm platelets ≥100,000/μL), a routine coagulation profile, von Willebrand's factor (vWF) activity in high-risk breeds, and a buccal mucosal bleeding time. Animals suspected to have acquired bleeding tendencies should be treated with vitamin K₁ (0.5–1.0 mg/kg, SC or IM) at 0, 12, and 24 hr before tissue sampling. If buccal mucosal bleeding time is >5 min, a fresh frozen plasma transfusion is indicated. An additional treatment with desmopressin acetate (DDAVP, 0.3–1 μg/kg diluted in saline), increases plasma vWF 2-fold over baseline within 1 hr as well as plasma activity of factor VIII. DDAVP can initiate a hemostatic effect in dogs with type 1 vWF (partial quantitative deficiency) but not in those with disease caused by qualitative defects or complete vWF deficiency.

Last full review/revision March 2012 by Sharon A. Center, DVM, DACVIM