The liver is an amazingly complex organ and is responsible for multiple functions in the body, all of which are vital for good health. Such multi-tasking means that there are a number of things that can go awry. It’s not surprising then that canine liver disease is so common.
The liver happens to be remarkably resilient and, to a great extent, can regenerate and restore itself following damage. Additionally, because the liver contains multiple lobes, significant disease in only one or two of them doesn’t typically impair liver function.
Before blood from the abdominal organs travels back to the heart, it must first pass through the liver via a large vessel called the portal vein. Once within the liver, hepatocytes (liver cells) detoxify the blood, removing any undesirable substances such as toxins or bacteria. This detoxification process is the reason a dog can recover from “food poisoning” after dining on a rotten carcass.
In addition to its role as the “garbage disposal” of the body, the liver also acts as a manufacturing plant, producing substances such as proteins, fatty acids, glucose, cholesterol, and blood clotting factors. These essential products are released from the liver into the bloodstream for use throughout the body.
The liver serves as a storage unit for several essential nutrients, vitamins, minerals and glycogen, an important source of energy release during exercise. The liver also produces bile (bilirubin) and stores it within the gallbladder so it is ready for release into the small intestine when needed for fat digestion.
Symptoms of liver disease
There is no classic combination of symptoms that alerts one to the diagnosis of liver disease. Rather, many liver-related symptoms overlap with those of other illnesses. Symptoms can range from single to multiple, and from mild to severe. Believe it or not, some dogs with significant liver disease demonstrate no overt abnormalities whatsoever (one of the many reasons routine canine senior citizen blood screening is a really good idea).
The more common liver disease-associated symptoms include:
- loss of appetite
- increased thirst
- abdominal distention caused by fluid accumulation
- neurological abnormalities (hepatic encephalopathy)
There are typically two stages of testing involved in diagnosing liver disease. While the first stage confirms that a liver abnormality is present, this testing doesn’t hone in on the clear-cut cause of the problem. All it says is that some type of liver disease is. The second stage of testing is used to confirm the exact type of liver disease present. A liver biopsy is often needed to make this distinction although, on occasion, the ultrasound alone is confirmatory. A liver biopsy is an invasive procedure. It’s potential risks and benefits must be carefully evaluated before proceeding, particularly with dogs whose health is significantly compromised.
First stage testing
- thorough physical exam
- complete blood cell count (CBC)
- chemistry profile
- bile acids test
- blood clotting studies
- abdominal x-ray
Second stage testing
- abdominal ultrasound
- liver biopsy collected via surgery, laparoscopy, or with ultrasound guidance
How liver function is assessed
Several different blood tests are utilized when diagnosing liver disease. The chemistry profile measures ALT (alanine aminotransferase) and AST (aspartate aminotransferase), enzymes contained within the liver cells. Elevations of these two enzymes indicate that at least some of the liver cells are “unhappy,” enough so that they are leaking excess ALT and AST into the bloodstream. This is really the only information provided by these two enzymes. They don’t reveal anything about how the liver is functioning. In other words, one could not diagnose liver failure on the basis of ALT and AST results. Unfortunately, measurements of these two enzymes are often referred to as “liver function tests,’ a term that I believe to be very misleading. (Okay, I’ll jump off of my soapbox.)
So, how then does one evaluate liver function? The chemistry profile also measures albumin, glucose, urea, and cholesterol all of which are manufactured within the liver. Decreased amounts of these four substances in the bloodstream are indicators that liver function is impaired.
Blood clotting factors are also made within the liver, and abnormally prolonged blood clotting times are consistent with liver dysfunction. A bile acids test is yet one more way of screening for impaired liver function.
Stay tuned for Liver Disease: Part II to learn about the causes and treatment of liver disease.
Have you cared for a dog with liver disease? If so, how did things turn out?