Introduction
Liver disease is a serious diagnosis, but it is not necessarily a death sentence for your dog. Because the liver is involved in so many diverse bodily functions, your veterinarian is likely to recommend a battery of tests to assess the condition of your dog’s liver, including a complete blood count (“CBC”), serum biochemistry profile, serum bile acid test, urinalysis, fecal analysis and survey abdominal radiographs or ultrasound. If the results of these tests suggest liver disease, other tests may follow to confirm the diagnosis. The liver is an amazing organ with a large reserve capacity, and upward of 70 percent of functional liver tissue must be damaged before actual liver failure can be diagnosed. The key is to catch liver disease early, so that an appropriate treatment plan can be put in place to prevent progression of the disease into liver failure.
Diagnosing Liver Disease in Dogs
First, your veterinarian will conduct a thorough physical examination of your dog, checking for a distended abdomen, pale mucous membranes, poor coat condition, dehydration, signs of jaundice or neurological changes. She may be able to palpate an enlarged liver or an identifiable mass in the front part of the abdomen. She also will take a thorough history. Be sure to tell your veterinarian if you have noticed any of the clinical signs that have been associated with liver disease, such as loss of appetite, depression, lethargy, weakness, weight loss, changes in coat condition, nausea, vomiting or diarrhea. Tell your veterinarian if you have noticed changes in the volume or color of your dog’s urine or stools, and if so what those changes are. Tell her if your dog has shown changes in behavior or other neurological signs, like aggression, dementia, hysteria, trembling, circling, ataxia (lack of muscular coordination), staggering, pacing, head-pressing, vision problems, excess salivation, tremors, generalized seizures or loss of consciousness.
The next diagnostic step probably will be a series of blood tests. Blood samples will undergo a comprehensive blood cell count and serum chemistry panel to assess the levels of certain liver enzymes and other substances, including albumin, blood urea nitrogen, bilirubin, cholesterol, glucose and electrolytes, among others. The primary enzymes your veterinarian will assess are alanine transaminase (ALT) and aspartate transaminase (AST), although she also may look at levels of alkaline phosphatase (AP) and gamma glutamyltransferase (GGT). Dramatic elevations in liver enzymes do not necessarily correlate with the severity of liver dysfunction, and likewise serious liver disease can exist in dogs with only mild liver enzyme changes.
Another diagnostic tool is a serum bile acid concentration test. This involves taking one blood sample after the dog has fasted for 12 hours, and another 2 hours after a high-fat meal, and then testing both samples for bile acid levels. Elevated serum bile acid reflects clinically relevant liver disease. With widely available, rapid and simple methods for determining serum bile acid concentration, this is a convenient and practical test of liver function in dogs.
A urine sample should also be analyzed routinely when liver disease is suspected, particularly for the presence of excess bilirubin and/or ammonium biurate crystals. A urinalysis will also help your veterinarian check your dog’s kidney function. While fecal evaluation itself rarely provides helpful information about suspected liver disease, it can be important if there are significant changes in color. Pale, pasty stools indicate complete bile duct obstruction. Dark, red or orange-colored feces can indicate gastrointestinal bleeding or increased bilirubin production.
Although not part of the standard screening protocol described above, another good test of liver disease is fasting plasma ammonia concentration. Special procedures and laboratories are required for this test, but they are becoming increasingly available. Elevated plasma ammonia levels reflect hepatobiliary disease in that the diseased liver cannot detoxify ammonia from the blood.
Further diagnosis measures may include coagulation profiles, abdominocentesis/fluid analysis, survey abdominal radiographs (x-rays) or an ultrasound examination. Veterinary teaching hospitals and large referral practices may be able to perform other diagnostic imaging procedures, including nuclear imaging (scintigraphy), magnetic resonance imaging (MRI) or computed tomography (CT scan).
Finally, your veterinarian may recommend a fine needle aspirate of the liver and/or a liver biopsy in order to definitively diagnose liver disease and assess your dog’s prognosis. There are a number of ways to obtain a liver biopsy, including laparoscopically. The best technique will be determined by your veterinarian based on whether she believes that the disease is generalized or focal, assessment of your dog’s coagulation status and the animal’s clinical stability and fitness for undergoing general anesthesia. Of course, a biopsy is an invasive procedure carrying its own inherent risks – including the risks associated with anesthesia and infection, and very importantly the risk of hemorrhage in animals with preexisting coagulation problems.
Diagnosis liver disease in dogs requires a battery of tests usually conducted over an extended period of time. Using a combination of history, physical examination, blood/urine/fecal tests, coagulation profiles, diagnostic imaging and tissue sampling, your veterinarian should be able to pinpoint the nature and extent of the liver condition, so that appropriate treatment can be provided.