Your dog's blood work comes back and your veterinarian reports that the liver enzymes are elevated. What does this mean and do you need to be concerned? It can certainly be concerning and overwhelming when your dog's blood work comes back with elevated liver enzymes. However, it's essential to understand that elevated liver enzymes in dogs are not a disease, but rather a sign that something is going on with the liver. The liver is a vital organ responsible for various metabolic functions, including detoxification and protein synthesis. When the liver is affected, it can lead to an increase in liver enzymes in the blood. There are many possible causes of elevated liver enzymes in dogs, ranging from benign conditions to severe diseases. In this article, we'll explore the different causes of elevated liver enzymes in dogs so you can have a better understanding of what is going on with your dog.

What are liver enzymes?

Liver enzymes are proteins produced by the liver that help carry out various metabolic functions in the body. These enzymes are responsible for breaking down and metabolizing different substances such as drugs, metabolites, and toxins.

In dogs, the most commonly measured liver enzymes in blood tests are alanine transaminase (ALT), aspartate transaminase (AST), and alkaline phosphatase (ALP).

ALT and AST are enzymes that are present in the liver cells, and their levels in the blood increase when there is damage or inflammation in the liver. AST is also found in skeletal muscle. ALP, on the other hand, is an enzyme that is present both in the liver and bones.

An increase in ALP levels in the blood can indicate liver damage or disease, as well as bone growth secondary to certain medications such as prednisone and phenobarbital.

While it is important to understand that not all elevations in liver enzymes in dogs are suggestive of liver disease, in most cases, elevated liver enzymes in dogs are a sign that there is something going on in the liver, and further diagnostic testing is required to determine the underlying cause. It's important to keep in mind that elevated liver enzymes in dogs are not a specific diagnosis, but rather an indication that something is affecting the liver.

What causes elevated liver enzymes in dogs?

There are many reasons for high liver enzymes in dogs. Veterinarians typically separate them into two categories: hepatic and extrahepatic.

Primary causes of elevated liver enzymes in dogs

Hepatic causes of high liver enzymes in dogs refer to conditions that affect the liver directly, leading to liver damage and subsequent increases in liver enzymes. Some common hepatic causes of elevated liver enzymes in dogs include:

  • Hepatitis: Hepatitis refers to inflammation of the liver and can be caused by viral, bacterial, or inflammatory factors.
  • Benign nodular hyperplasia: Benign nodular hyperplasia is a condition commonly seen in older dogs in which the liver develops multiple small non-cancerous nodules.
  • Drug-induced: Certain drugs, such as steroids (e.g. prednisone) and phenobarbital, can cause elevated liver enzymes in dogs, especially ALP.
  • Congenital liver diseases: Certain liver diseases, such as portosystemic liver shunts and copper storage diseases, are inherited and can cause liver enzyme levels to increase.
  • Toxins: Certain toxins can induce the activity of liver enzymes in dogs. These can include xylitol, aflatoxins, and lead toxicity for example.
  • Cholangitis: Cholangitis refers to inflammation of the bile ducts that carry bile from the liver to the small intestine. It can cause liver damage and elevated liver enzymes.
  • Cirrhosis: Cirrhosis is a chronic liver disease that leads to scarring and permanent damage to the liver. It can be caused by chronic infections, exposure to toxins, or chronic active hepatitis.
  • Liver cancer: Diffuse cancer in the liver, whether malignant or benign, can cause liver enzyme levels to increase. Common cancers that can affect the liver include lymphoma, carcinoma, and hemangiosarcoma.

Secondary causes of elevated liver enzymes in dogs

Secondary, or extrahepatic causes of elevated liver enzymes in dogs refer to conditions outside the liver that can affect liver enzyme levels. Some common extrahepatic causes of elevated liver enzymes in dogs include:

  • Pancreatitis: Pancreatitis is inflammation of the pancreas and can cause liver enzyme levels to rise due to inflammation spreading to the liver.
  • Diabetes: Dogs with diabetes can have elevated liver enzymes due to the negative metabolic state (subclinical hepatic lipidosis).
  • Cushing's disease: Dogs with Cushing's disease, or hyperadrenocorticism, can have elevated liver enzymes due to excess steroid production leading to swelling of the liver.
  • Heart disease: Right-sided heart disease can cause liver congestion, leading to elevated liver enzyme levels.
  • Inflammatory bowel disease: Inflammatory bowel disease (IBD) can cause elevated liver enzyme levels due to inflammation in the gastrointestinal tract.

These illnesses can lead to a benign reactive/vacuolar hepatopathy, causing an increase in liver enzymes but normally there is no impact on the functioning of the liver.

How to determine if your dog’s elevated liver enzymes are of concern

If your vet tells you that your dog has elevated liver enzymes and is not on any medications that would cause the elevations such as prednisone or phenobarbital, nor does your dog have Cushing's disease that would explain the increases, here are some options that I would recommend to consider:

  • Liver function test: A bile acid blood test can evaluate liver function and performance. If they are high, it suggests liver impairment.
  • Medication trial: Antioxidants like SAMe or medications like ursodiol can support liver health. I then recommend rechecking the liver enzymes in 30 days.
  • Recheck: If your dog is symptom-free, rechecking levels in a few months might be suggested.
  • Imaging: X-rays or ultrasound can assess the liver for evidence of infection, inflammation, or tumors.
  • Liver biopsy: For more serious concerns, a biopsy may be recommended for further analysis.

Do all elevated liver enzymes need to be investigated further?

No, elevated liver enzymes in dogs do not always need to be investigated further. In mild cases of elevated liver enzymes, your veterinarian may recommend periodic blood testing to start trending the values before recommending further testing. Generally speaking, liver enzyme values greater than 2-3 times the upper limit of normal should be investigated as they can indicate a more serious condition. This is also assuming the dog is asymptomatic and there are no abnormalities on its physical exam.

Certain medications such as corticosteroids (prednisone) and phenobarbital will predictably cause elevated liver enzymes in dogs, especially the ALP. In these cases, the elevated liver enzyme values are not indicative of liver disease and will usually resolve with the discontinuation of the medication.

Additionally, young dogs with an elevated ALP may not need to be investigated further as this could be due to skeletal growth and development. Your veterinarian may recommend periodic blood testing to ensure the elevated liver enzyme values do not persist or cause any issues.

Finally, elevated liver enzymes in dogs can be observed as part of an aging process, as normal age-related changes occur to cause increased activity of certain enzymes. Examples include nodular and vacuolar hepatopathy. In this case, your veterinarian may recommend periodic blood testing every 4-6 months.

Elevated liver enzymes in dogs can be caused by a variety of conditions, both within and outside the liver. The most common causes of elevated liver enzymes in dogs are due to medications like prednisone, Cushing's disease, liver inflammation such as hepatitis, and benign, age-related changes.

In mild cases of elevated liver enzymes, periodic blood testing may be all that is needed to ensure there are no more serious underlying issues. However, if your dog’s elevated enzyme levels persist or become particularly high (greater than 2-3 times the upper limit of normal), further investigation should be done as soon as possible. Additionally, if your dog's high liver enzymes are due to medications such as corticosteroids and phenobarbital, they will go back into normal range with discontinuation of the medication.

Finally, elevated liver enzymes in young dogs could be due to skeletal growth and development, or part of an aging process. It is important to work with your veterinarian to determine the best course of action for your individual dog.