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Biochemical evaluation of the hepatobiliary system in dogs and cats
1Veterinary Clinical Pathology, Murdoch University School of Veterinary Studies, Western Australia.
Insights
Diagnosing liver disease requires laboratory tests to assess function and type. Hepatic enzymology detects active disease, while function tests like serum bile acids are crucial for accurate diagnosis in animals.
Area of Science:
- Veterinary Medicine
- Biochemistry
- Hepatology
Background:
- Hepatobiliary disease presents with diverse clinical signs, often necessitating laboratory diagnostics to confirm liver involvement.
- Understanding functional anatomy and pathophysiology is key to selecting appropriate tests for liver disease assessment.
- Hepatic enzymology is a primary tool, differentiating hepatocellular (leakage enzymes like ALT) and cholestatic (induced enzymes like ALP) patterns.
Purpose of the Study:
- To outline the principles and methods for laboratory diagnosis of hepatobiliary disease.
- To emphasize the importance of integrating enzymology with liver function tests for comprehensive assessment.
- To guide the selection of diagnostic tests for determining the type, duration, and functional status of liver conditions.
Main Methods:
- Utilizing hepatic enzymology to detect hepatocellular (e.g., SDH, GLDH, ALT) and cholestatic (e.g., ALP, GGT) patterns.
- Employing screening tests of hepatic function including albumin, protein, bilirubin, glucose, and urea.
- Performing urinalysis for bilirubinuria, urobilinogenuria, and ammonium biurate crystals.
- Evaluating blood coagulation profiles when surgery or bleeding is a concern.
- Assessing hepatobiliary function using paired pre- and post-prandial serum bile acids (preferred in dogs and cats).
- Considering Bromosulphalein (BSP) dye clearance tests for functional assessment, though less sensitive than serum bile acids for certain conditions.
Main Results:
- Enzymology can identify active liver disease but may not reflect disease severity or functional impact.
- Screening liver function tests are essential for a complete biochemical database.
- Serum bile acids and ammonia tolerance tests are more sensitive for detecting portosystemic anomalies than BSP clearance.
- Urinalysis and coagulation tests provide supplementary diagnostic information.
Conclusions:
- A multi-faceted laboratory approach combining enzymology and function tests is necessary for accurate hepatobiliary disease diagnosis.
- The choice of tests should be guided by clinical signs and the need to establish disease type, duration, and functional status.
- Serum bile acids are the preferred method for assessing liver function in companion animals.
Abstract:
The causes and clinical signs of hepatobiliary involvement in disease are many and varied and often are not referable directly to this organ system. Laboratory investigation frequently is necessary to rule hepatic disease in or out, to assess the functional impact on the liver, and to decide whether hepatic disease is the patient's primary problem or a complication of something else. The selection and interpretation of laboratory tests to resolve these problems is based on an understanding of relevant functional anatomy and pathophysiology. The mainstay of such assessment is hepatic enzymology, which can detect active disease in both hepatocytes and the biliary system. The hepatocellular pattern of disease is characterized by increases in leakage enzymes such as SDH, GLDH, and ALT and the cholestatic pattern by increases in induced enzymes (ALP and GGT). In general, enzymology does not allow the intensity or functional effect of hepatobiliary disease to be assessed, and quite severe hepatopathies may have only minimal enzyme abnormalities. For this reason, the primary biochemical data base for ruling hepatobiliary disease in or out always should involve some screening tests of hepatic function, such as albumin, protein, bilirubin, glucose, or urea determinations; as well as urinalysis to search for bilirubinuria and urobilinogenuria in hyperbilirubinemic patients and for ammonium biurate crystals when hyperammonemia or hepatic encephalopathy is suspected. Because the liver synthesizes most clotting factors, evaluation of blood coagulation is indicated when surgery is contemplated on patients with liver disease or when bleeding is present. Paired pre- and post-prandial determinations of serum bile acids are the preferred method for assessment of hepatobiliary function in dogs and cats. However, the BSP clearance test continues to be useful in the functional assessment of the liver as long as the dye remains available to veterinarians. Clearance of BSP is delayed in hepatocellular, cholestatic, and portosystemic disease as well as by severe extrahepatic circulatory disturbances, In general, this functional test is less sensitive than serum bile acids or the ammonia tolerance test in the recognition of hepatic encephalopathy caused by portosystemic anomalies. The objectives of biochemical screening of the liver are to establish the type (hepatocellular, biliary, or mixed), duration (acute, chronic), and stage (aggressive, convalescent) of hepatobiliary disease and to assess functional status.(ABSTRACT TRUNCATED AT 400 WORDS)