When presented with a dog that just “ain’t doing right” (in veterinary speak, a dog that is “ADR”), the first thing that most veterinarians will do is take a complete history of the dog’s background from its owner and then conduct a thorough physical examination. She will be looking for any observable abnormalities, such as distended abdomen, pale mucous membranes, poor coat condition, dehydration, signs of jaundice, behavioral changes and/or neurological changes. She may be able to palpate (feel) an enlarged liver or an identifiable mass in the front part of the dog’s belly (abdomen).
It is extremely important for an owner to tell his veterinarian about any unusual behaviors or actions that he has noticed in his dog, such as appetite loss, depression, lethargy, weakness, lack of coordination, weight loss, changes in coat condition, nausea, vomiting or diarrhea. The owner should tell the veterinarian about any changes in the volume or color of his dog’s urine or stools, and if so what those changes are. He should discuss any changes in behavior or other neurological signs, such as aggression, dementia, hysteria, trembling, circling, ataxia (lack of muscular coordination), staggering, pacing, head-pressing, vision problems, excess salivation, seizures or loss of consciousness.
The next diagnostic step probably will be a series of blood tests, including a complete blood count (CBC) and a serum biochemistry panel. Blood samples are easy to obtain and will undergo comprehensive assessment of the circulating levels of certain liver enzymes and other substances, including albumin, blood urea nitrogen (BUN), bilirubin, cholesterol, glucose and various electrolytes, among other things. The primary enzymes that the veterinarian will assess are alanine transaminase (ALT) and aspartate transaminase (AST), although she also probably will look at the levels of alkaline phosphatase (AP) and gamma glutamyltransferase (GGT). Dramatic elevations in these enzymes usually reflect liver dysfunction, although they do not necessarily correlate with the severity of liver disease. Similarly, serious liver disease can exist in dogs with only mild liver enzyme changes.
Another important 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 it is fed a high-fat meal. Both samples are then tested for bile acid levels. Elevated serum bile acid levels are highly suggestive of 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 domestic dogs.
A urine sample will also be analyzed routinely when liver disease is suspected. The veterinarian will look for the presence of bilirubin and/or ammonium biurate crystals in the sample. The urinalysis will help the veterinarian assess the dog’s kidney function. While fecal evaluation rarely provides diagnostic information about liver disease, it can be helpful if there are significant changes in the texture or color of the stool. Pale grey, pasty stools suggest complete bile duct obstruction. Dark red or orange-colored feces can indicate gastrointestinal bleeding or increased bilirubin breakdown, which also frequently accompany liver disease.
Although it is not part of the standard screening protocol described above, another test of liver disease is assessment of the dog’s fasting plasma ammonia concentration. Special procedures and laboratories are required for this test, but they are becoming increasingly available to general veterinary practitioners. Elevated plasma ammonia levels after fasting suggest hepatobiliary disease, because a severely damaged liver cannot detoxify and remove ammonia from the blood. A nother confirmatory (but rarely used) test is an ammonia tolerance test, which can be helpful in distinguishing between liver and gall bladder disease.
More advanced diagnostic measures include blood coagulation profiles, abdominocentesis (analysis of free fluid sampled from the abdominal cavity), survey abdominal radiographs (X-rays) and/or ultrasound examination. Veterinary teaching hospitals and large referral practices may be able to perform even more specialized diagnostic imaging procedures, such as nuclear imaging (scintigraphy), magnetic resonance imaging (MRI) and/or computed tomography (CT/CAT scan).
The attending veterinarian may recommend a fine needle aspirate of the liver and/or a liver tissue biopsy in order to definitively diagnose liver disease and assess the dog’s prognosis. There are a number of ways to obtain a liver sample, including laparoscopy. The best technique will be determined by the veterinary team based upon whether they believe that the dog’s liver disease is generalized or focal. The decision also will be based on the dog’s blood coagulation status, clinical stability and fitness for undergoing general anesthesia. A biopsy is an invasive procedure that carries its own inherent risks – including those associated with anesthesia, seeding of infection and hemorrhage in animals with preexisting coagulation disorders. Biopsy samples are submitted to a laboratory for culture and histopathological examination.
Diagnosing liver disease in dogs requires a number of tests that typically are conducted in a specific order over an extended period of time. Using a combination of history, physical examination, blood/urine/fecal tests, coagulation profiles, diagnostic imaging and tissue sampling, a veterinarian should be able to assess the nature and extent of a dog’s liver condition, so that an appropriate treatment protocol can be implemented.