Diseases of the Liver and Biliary Tract

Chapter 71 Diseases of the Liver and Biliary Tract


The liver has many diverse functions related to hepatic blood flow; protein, carbohydrate, and fat metabolism; detoxification and excretion of drugs and toxins; and formation and elimination of bile. Consequently, the clinical and laboratory abnormalities associated with liver failure are diverse.

Clinical Signs

Clinical signs of liver disease include those typically associated with hepatic dysfunction, such as jaundice, hepatic encephalopathy (HE), ascites, and excessive bleeding, and nonspecific signs such as vomiting, diarrhea, anorexia, lethargy, and weight loss, which overlap with signs of other body system disorders.

Signalment and History

Physical Examination

Routine Laboratory Evaluations

Because clinical findings in hepatobiliary disease often are vague, hepatic disease may not be suspected until biochemical tests identify elevated liver enzyme activity or other evidence of hepatic dysfunction (e.g., hyperbilirubinemia or hypoalbuminemia). Liver function studies such as serum bile acid (SBA) concentrations are used to achieve the following:

Findings consistent with liver disease on routine laboratory tests are described below.

Liver Enzymes

Evaluation of serum liver enzyme activity is used as a screening test to detect liver disease. Increases in liver enzyme activity are not specific for the underlying hepatic disorder. However, liver enzymes can be used to categorize the underlying pathophysiologic mechanism. Increases in liver enzyme activity may occur secondary to hepatocellular injury and leakage (Fig. 71-1), or due to increased production stimulated by bile retention (cholestasis) or drug induction (Fig. 71-2).

Many systemic diseases can secondarily affect the liver (reactive hepatopathy), causing increased liver enzyme activity, but these are not necessarily associated with clinical liver disease. For example, feline hyperthyroidism is commonly associated with increased liver enzyme activity without significant hepatic dysfunction.

Alanine Aminotransferase

Increased alanine aminotransferase (ALT) activity indicates hepatocyte injury with leakage of enzyme from the cytoplasm of the hepatocyte (see Fig. 71-1). The magnitude of ALT increase generally correlates with the number of injured hepatocytes.

Alkaline Phosphatase

Increases in serum alkaline phosphatase (ALP) activity are due to accelerated production of this enzyme, stimulated by cholestasis or drug induction (see Fig. 71-2). ALP is a membrane-associated enzyme present in many tissues; however, only liver, bone, and corticosteroid-induced isoenzymes contribute to serum ALP activity. Serum ALP activity in normal dogs and cats is usually due to the liver isoenzyme. An increase in this type of ALP activity indicates intrahepatic or extrahepatic cholestasis.

Other Biochemical Tests

Numerous biochemical tests can be altered by liver disease, including serum bilirubin, albumin, globulin, urea nitrogen, glucose, and cholesterol. Many of these parameters reflect some aspect of liver function; however, they lack sensitivity or specificity for liver disease.

Liver Function Tests

Liver function tests can document clinically significant hepatic dysfunction when liver disease is suspected, based on historical, clinical, laboratory, and radiographic findings. SBA determinations have largely replaced the use of organic anion dyes such as sulfobromophthalein (Bromsulphalein) and indocyanine green (ICG). Blood ammonia concentration and ammonia tolerance tests can specifically evaluate the portal circulation (for portosystemic shunts) and detect HE.

Serum and Urine Bile Acids

The normal physiology of bile acid metabolism is shown in Figure 71-3A In health, bile acids are confined to the enterohepatic circulation, and systemic concentrations are low. SBA concentrations increase in the systemic circulation with all types of liver disease (Fig. 71-3B). Because the liver has a large reserve capacity for synthesis of bile acids, even severe hepatic dysfunction does not cause decreased SBA concentrations.

Fasting Serum Bile Acid Concentration

A fasting serum bile acid (FSBA) concentration obtained after a 12-hour fast is a sensitive, specific measure of hepatobiliary function in dogs and cats. Normal FSBA values in dogs and cats are <20μmol/L. When concentrations exceed 30μmol/L, a liver biopsy may be warranted to evaluate the underlying liver disease.

Postprandial Serum Bile Acid Concentration

Postprandial serum bile acid (PPSBA) concentration is an endogenous challenge test of liver function. Whether PPSBA concentration is a more useful diagnostic test than FSBA concentration remains unclear. In dogs, similar information is provided by either test in most hepatobiliary disorders. Notable exceptions include dogs with portosystemic shunts or cirrhosis, because with these disorders, FSBA can be in the normal range. In cats, the diagnostic efficacy of PPSBA exceeds that of FSBA for all hepatic disorders, including portosystemic shunts. For best diagnostic utility, paired FSBA and 2-hour PPSBA is recommended. To perform the PPSBA concentration test, take the following steps:

Parameters of Hemostasis

The liver plays a central role in the coagulation and fibrinolytic systems. The liver is responsible for synthesis of all coagulation factors except factor 8, von Willebrand factor. Fibrinogen, antithrombin, and protein C are all synthesized in the liver and can be decreased with hepatic dysfunction. Activated coagulation factors and fibrinolytic enzymes are also cleared by the liver.

Diagnostic Imaging

Liver Biopsy

Liver biopsy often is required to definitively characterize the nature and severity of hepatic disease, to differentiate acute from chronic disorders, and to assess response to therapy. Selection of the best procedure for obtaining a liver biopsy depends on numerous factors, including liver size, presence of coagulopathy, diffuse versus focal hepatic lesions, presence of biliary tract obstruction, presence of other intra-abdominal abnormalities, likelihood of surgical resection of a mass, tolerance of general anesthesia, available equipment, and expertise of the clinician.

Biopsy Methods

Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Diseases of the Liver and Biliary Tract

Full access? Get Clinical Tree

Get Clinical Tree app for offline access