Canine Liver Enzymes: Choosing the Right Path for Diagnosis

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Filed Under: Internal Medicine

Canine Liver Enzymes:  Choosing the Right Path for Diagnosis

Valerie Case, DVM (Diplomate ACVIM - Internal Medicine)

Interpreting canine liver enzymes can be very challenging.  Reversible but severe elevations can occur with administration of certain drugs, while diffuse neoplasia may be present in the liver without causing any enzyme changes.  This article summarizes the guidelines our Internal Medicine Department uses to evaluate canine liver enzymes.

Alkaline phosphatase (ALP) has high sensitivity but low specificity for hepatobiliary disease.  Elevation of ALP alone without other enzyme abnormalities is most often associated with drug induction, hyperadrenocorticism, and benign reactive changes within the liver including nodular hyperplasia and vacuolar hepatopathy.  Occasionally ALP is the only abnormal enzyme in patients with hepatic neoplasia.  If a patient’s history does not support exposure to ALP inducing drugs or endocrine disease, monitoring the ALP over time is an acceptable course of action in asymptomatic patients.  If the ALP elevation persists or is progressive over 4-6 weeks, abdominal ultrasound and liver function testing is recommended for further investigation.  Our on-site laboratory can measure both serum bile acids and blood ammonia levels.

Gamma glutamyl transferase (GGT) has greater specificity for hepatobiliary disease compared to ALP.  When both GGT and ALP are elevated, the specificity for liver disease nears 100%.  Gall bladder and bile duct disease will cause the largest elevations in GGT.  The combination of increased GGT, ALP, total bilirubin, and cholesterol should be immediately concerning for biliary tract obstruction, and warrants referral for abdominal ultrasound and critical care management.

Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) increase due to leakage from damaged hepatocytes.  Mild elevations can occur with diseases outside of the liver including pancreatitis, gastroenteritis, congestive heart failure, and endocrine diseases.  Toxic and infectious hepatitis generally cause the largest elevations of ALT and AST due to widespread hepatocyte inflammation and necrosis.  A thorough history exploring risk of exposure to known hepatotoxins as well as testing for Leptospirosis are indicated in these cases.  AST elevation exceeding ALT may indicate muscle cell damage rather than liver disease.  Evaluation of creatine kinase (CK) can help to differentiate.

Abdominal radiographs are excellent for evaluating hepatic size and screening for mineralization or gas within the parenchyma or biliary tree.  Abdominal ultrasound can determine if disease is focal or diffuse, as well as evaluate the biliary system and portal vasculature.  In some cases extrahepatic portosystemic shunts can be visualized, but should always be confirmed with portal scintigraphy.  Fine needle aspiration can be diagnostic when focal lesions are present, or when the liver is enlarged with diffuse parenchymal changes (hepatic lipidosis, lymphoma).  Patients with suspected chronic or chronic active hepatitis require liver biopsy for definitive diagnosis.  Biopsies obtained via laparotomy or laparoscopy are recommended over ultrasound guided techniques.  We offer laparoscopic liver biopsy for patients over 20 pounds body weight.

Our Internal Medicine Team is proud to offer extensive diagnostic testing and care for your Patients with hepatic disease.  Call our Client Service Representatives today to schedule your Patients!