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The liver plays an important role in hundreds of diverse metabolic activities with innumerable physiological consequences, including synthesis of plasma proteins; catabolism and storage of carbohydrates; synthesis, degradation and storage of lipids; detoxification and excretion of many toxic agents; and the formation and elimination of bile.

Due to the prevalence of liver disease, the ability to promptly evaluate liver function is an extemely valuable tool to a veterinarian, as many liver diseases are treatable if diagnosed early.

A thorough and methodical approach is necessary when evaluating the liver, and should include the following:

History

• Age and breed of the pet
• Clinical signs associated with liver disease can include, but are not limited to, depression, anorexia, weakness, weight loss, diarrhoea, fever, icterus, polyuria/polydipsia.
• Clinical signs associated with hepatic encephalopathy can include, but are not limited to, listlessness, disorientation, abnormal personality or behaviour changes, and seizures.
• Medications or supplements being given

Physical Exam

• May present with hepatomegaly, enlarged lymph nodes, haematomas, fever, icterus and jaundice

Blood Chemistries

• Liver enzymes—ALT, AST, ALKP, LDH and GGT are used to screen for the presence of hepatobiliary disorders. Serum enzymes lack specificity as to the nature and severity of the disorder—they are not liver-function tests.
• Bilirubin—Total bilirubin is used to classify jaundice as prehepatic, hepatic or posthepatic. Bilirubin is less sensitive, but more specific, than liver enzymes in identifying hepatobiliary disease.
• Albumin—Albumin is made exclusively by the liver. Decreased levels from synthetic failure ensue when 70% of hepatobiliary function has been compromised.
• Cholesterol—Decreased concentrations can occur with congenital or acquired portosystemic shunts and acute hepatic failure. Increases in a jaundiced patient usually indicate major bile duct occlusion, particularly in cats. Cholesterol concentrations are also increased in nonhepatic diseases such as pancreatitis, diabetes mellitus, hyperadrenocorticism and hypothyroidism, which, if present concurrently, can confuse interpretation.

Liver-Function Tests

• Bile Acids—Bile acids concentration is a sensitive and specific indicator of hepatic function in dogs and cats. However, the magnitude of elevation does not distinguish the cause of disease because of the wide overlap among disease processes.
• Ammonia—Although not as sensitive for hepatic disease, in cases of inadequate liver function, ammonia is not converted to urea, and plasma ammonia levels rise. Correct sample handling and immediate testing are crucial for accurate results.

Radiography and Ultrasonography

• Can be used to determine the size and density of the liver
• Evaluate supporting circulatory structures

Liver Biopsy

• Definitive diagnosis of liver disease is histologic evaluation of liver tissue.

Haematology

• Mild, nonregenerative anaemia
• The white blood cell count may be normal, elevated or decreased, depending on the cause of the hepatic insult.

Symptoms of liver disease are variable and subtle in the early stages. The classic symptoms are poor appetite or anorexia, weight loss, lethargy and anaemia.

Other sympotoms include:

• Polyuria/Polydipsia (excess urinating and excess drinking of water)

• Light-coloured stool—if the biliary tree is prevented from secreting normal bile into the intestine, the stool will lack the bile pigmentation and appear lighter in colour.

• Bleeding disorders—the normal clotting system can be impaired since it depends on a healthy liver.

• Distended abdomen due to ascites or hepatomegaly—breathing might be laboured from pain or pressure on the diaphragm.

• Vomiting, nausea and/or diarrhoea—blood may be present in the vomitus, especially if a gastric ulcer is present.

• Orange-coloured urine or mucous membranes due to jaundice

• Behavioural changes, such as circling, head tilt, head pressing and seizures, particularly right after a meal