Liver Function Tests

• Serum bilirubin, especially when >51 µmol/L (3 mg/dL).
• Biomarkers that change late in disease include glucose, cholesterol, blood urea nitrogen, albumin.
• Aminotransferase enzymes:
• ALT: half-life in cats is 3–6 hours (vs. 60 hours in dogs); hemolysis & lipemia will cause false elevations.
• AST: liver, skeletal & cardiac muscle; half-life in cats is ∼1 hour (vs. 12 hours in dogs).
• Cholestatic enzymes:
• ALP: bone, kidney, intestine, liver; half-life in cats is 6 hours (vs. 66 hours in dogs).
• GGT: kidney, pancreas, intestine, liver; half-life probably <1 hour.
• Induction of liver enzyme increases secondary to drugs (corticosteroids, phenobarbital) rare in cats compared to dogs.

Diagnostic Approach

• Most common liver diseases in cats are cholangitis syndrome, hepatic lipidosis, neoplasia; other causes include parasites, FIP, abscess, amyloidosis, cystic disease, acute toxic insult, etc.
• Minimum database (complete blood count, serum chemistry panel, total T4, urinalysis, FeLV/FIV): necessary to determine if elevations are hepatic or non-hepatic in origin.
• Gastrointestinal function tests: cobalamin, folate, fTLI, fPLI.
• Hepatobiliary causes of increases in ALT, AST include drugs, infection, inflammatory disease, inherited disease, neoplasia, portosystemic shunt, toxins, trauma.
• Non-hepatic causes of increases in liver enzymes include:
• Common: diabetes mellitus, hyperthyroidism, pancreatitis, inflammatory bowel disease, systemic infections (e.g., dental disease).
• Uncommon: congestive heart failure, severe hemolytic anemia, abdominal trauma, neoplasia.
• Serum bile acids can be used to confirm hepatobiliary disease is present (don’t perform if serum bilirubin is elevated); fasting (12 hours)+post-prandial (2 hours); does not give information on diagnosis or disease severity.
• Urine bile acids:creatinine ratio: single random urine sample (2 ml, no hematuria); ratio >4.4 is evidence of hepatic disease.
• Other diagnostic tests may be necessary to rule in/out hepatobiliary disease: imaging (radiographs, ultrasound), biopsy (percutaneous ultrasound-guided, laparoscopic, surgical laparotomy).
• Liver biopsy options:
• At least 6 portal areas necessary to diagnose inflammatory disease (∼15 mg tissue).
• Consider evaluation of coagulation, administration of vitamin K1 before biopsy.
• Fine needle aspirate: inexpensive, easy to perform; low risk, may only require sedation; small sample size (3–5 mg); only ∼50% agreement with histopathology; best for diffuse lesions such as lipidosis, lymphoma, fungal disease.
• Ultrasound-guided percutaneous needle core biopsy: requires general anesthesia; higher risk of liver trauma, fracture than with FNA, surgery, laparoscopy; use only manual or semi-automatic biopsy devices; good sample size, collect 2–3 samples from different lobes.
• Surgical or laparoscopic biopsy: best visualization but most invasive, largest sample size, multiple sites and organs can be biopsied; best ability to monitor sites for bleeding.
• Optimizing liver biopsy: collect multiple samples, collect bile for culture & cytology, give the pathologist a complete history.
• Contraindications for liver biopsy: platelets <80,000/mL, prolonged buccal mucosal bleeding time (>150 seconds), PT or APTT >2 times upper normal limit, infectious disease that could be disseminated, ascites.
• Post-biopsy patient care: monitor carefully for 6–12 hours (attitude, mucous membrane colour, capillary refill time, blood pressure, hematocrit), provide analgesia.

Non-Specific Treatments

• S-adenosyl-l-methionine (SAMe): ‘supernutrient’ for the liver, essential part of 3 major biochemical pathways, helps increase hepatic glutathione, no known contraindications, appears to be safe.
• Silymarin: antioxidant, free radical scavenger, inhibits effects of tumour necrosis factor, helps increase hepatic glutathione, no known contraindications, appears to be safe.