Reasons for Elevated Liver Enzymes in Dogs
By: Laura McLain Madsen, DVM
My dog’s liver enzymes are elevated. Now what should I do?
Elevated liver enzymes in dogs can cause your veterinarian to become concerned. But, perhaps your dog is acting fine, and the elevated liver enzymes show up on a routine blood panel. Or perhaps your dog is acting sick—maybe vomiting or not wanting to eat—and your vet has discovered liver enzyme abnormalities. Either way, you’re wondering what it means for your dog.
There are several enzymes that vets look at on a blood panel that can be related to dog liver disorders. Some of the enzymes are normally contained within the liver cells and are only released into the bloodstream if those liver cells are damaged. Other enzymes spill into the bloodstream if there is sluggish flow of bile from the liver to the intestines. Some of the enzymes are produced by other organs besides the liver.
As an organ, the liver has a variety of life-sustaining functions. It detoxifies the blood, produces bile to help digest nutrients in the intestinal tract, and makes important body proteins like albumin and clotting factors.
What are dog liver enzymes?
Enzymes are chemicals that perform important reactions in the body. In the context of blood testing, they are an indicator of a disease process occurring in an organ. The enzymes that veterinarians usually look at with regard to the dog's liver are called AST, ALT, ALKP and GGT.
AST (aspartate aminotransferase). This enzyme is stored in the liver cells as well as muscle cells. Damage to the liver (such as from a toxin or infection) that ruptures cells will allow AST to spill into the bloodstream. Similarly, damage to muscle cells (such as from trauma) will spill AST.
ALT (alanine aminotransferase). Like AST, the ALT enzyme resides within the dog's liver cells and is released into the blood with cell damage. Unlike AST, it is fairly specific for liver damage, as it is not produced by other organs in the dog's body.
ALKP (or ALP) (alkaline phosphatase). Whereas AST and ALT are elevated when there has been damage to liver cells, ALKP becomes elevated when the flow of bile from the liver to the gall bladder to the intestines is hindered. ALKP is also produced by intestines, bone, and kidney tissues. The bone variant of ALKP can be elevated in puppies (due to rapid bone growth) and in cases of bone disease, particularly bone cancer (osteosarcoma). Elevations of ALKP can also be induced by medications, particularly corticosteroids (prednisone, dexamethasone) and phenobarbital (an anticonvulsant). ALKP will also frequently be elevated in dogs with Cushing’s disease (hyperadrenocorticism), an overactive adrenal gland.
GGT (gamma glutamyl transpeptidase). Like ALKP, the GGT enzyme is an indicator of an abnormality in the flow of bile. Although GGT is also made by the dog's kidney and pancreas, an elevated blood level usually indicates a liver disorder.
It is important to realize that if there is permanent destruction of liver tissue and scarring (cirrhosis), the liver enzymes may actually return to near-normal levels. In advanced cases of liver failure, the ALT and AST could be normal, but other indicators of liver failure might be seen, such as low albumin, blood sugar, and clotting factors.
What are symptoms of dog liver problems?
Sometimes, there won’t be any obvious symptoms of a problem until liver disease is quite advanced. For this reason, many veterinarians recommend periodic wellness blood panels, to try to detect problems with your dog's liver and other organs before irreversible damage has been done.
General symptoms of liver problems include loss of appetite, vomiting, diarrhea, decreased activity level, and jaundice (a yellow hue to the white of the eyes, gums and skin). Other symptoms that may be seen with certain liver disorders include seizures, increased thirst, increased urination, behavioral abnormalities, distended belly, or pain in the front part of the abdomen.
What are causes of dog liver problems?
Many disorders can cause elevated liver enzymes in dogs. These include:
• Genetic problems: copper storage disease, in which the dogs have a genetic abnormality that allows copper to accumulate in the liver cells and damage them.
• Congenital problems (birth defects): portosystemic shunt. A shunt is an abnormal blood vessel that bypasses the liver, allowing blood to reach the brain without being detoxified. Symptoms include seizures, especially after meals, and poor growth in puppies.
• Endocrine problems: hyperadrenocorticism (Cushing’s disease, overactive adrenal gland), diabetes mellitus, and hypothyroidism (underactive thyroid gland).
• Disorders of the organs near the liver: pancreatitis (inflammation of the pancreas), cholecystitis (inflammation of the gall bladder), and intestinal disease.
• Problems that cause decreased blood flow to the liver: anemia, congestive heart failure, and shock.
• Trauma: being hit by a car or kicked.
• Infections: viruses (canine infectious hepatitis), bacteria (Leptospirosis, abscesses, bacterial spread from periodontal disease), dog parasites (heartworm; in severe cases the worms move “upstream” through the blood vessels from the heart to the liver)
• Cancer: hepatic carcinoma, lymphoma, hemangiosarcoma, and metastatic cancer.
• Drugs or medications: phenobarbital, non-steroidal anti-inflammatory drugs, sulfa antibiotics, antifungals, and cyclosporine.
• Toxins: xylitol (a sugar substitute), cycad (Sago) palm, Amanita “Death Cap” mushrooms, acetaminophen (Tylenol®), and blue-green algae.
• Autoimmune (when the immune system targets liver cells in error): chronic active hepatitis.
Are certain dog breeds at risk?
Some liver disorders, like toxins and infections, can strike dogs of any age or breed, but there are some breed dispositions for other liver diseases. Congenital shunts are more common in small breed dogs, especially Yorkshire terriers and Maltese. Chronic active hepatitis is more common in Labrador retrievers and Dobermans. Hemangiosarcoma strikes Golden retrievers and German shepherds. Liver failure due to carprofen (Rimadyl, a NSAID) is seen more commonly in Labradors, although is quite rare. Copper storage disease is seen in Bedlington, Skye and West Highland white terriers, Labradors and Dalmatians.
What tests can be done?
Elevated liver enzymes unfortunately don’t tell us exactly what is wrong with the liver, just that something is wrong with the liver. Further tests are necessary to clarify the exact problem.
Your veterinarian may recommend additional testing, including a complete blood count (CBC, to measure the red and white blood cell levels), urinalysis (to assess kidney function and look for crystals that could be related to liver disease), bile acids (a blood test measuring liver function), coagulation panel (to assess the clotting factors), x-rays, bacterial culture, ultrasound (to visualize the liver, looking for masses or inflammation), biopsy (to get a small piece of the liver tissue to send to a pathologist for an exact diagnosis), laparoscopy (scoping the belly to look directly at the liver), and blood levels of drugs like phenobarbital or toxins like copper.
What treatments are there?
Depending on the specific diagnosis there might be a variety of treatments used, such as antibiotics for infection or immunosuppressants for autoimmune disorders. In general, sudden-onset liver problems are often treated with intravenous fluids, anti-nausea medications, antibiotics, and pain medications. Surgery may be necessary to repair shunts or remove tumors.
For long-term management there are several liver-supporting medications that are useful. Silybin (silymarin, Marin®) is a chemical derived from the milk thistle plant that has antioxidant and liver cell protection qualities. SAMe (s-adenosyl-methionine) is a neutraceutical that enhances liver cell health, regeneration, and detoxifying abilities. SAMe is available in several products for dogs, including Denosyl® and Zentonil®, or in combination with silybin in Denamarin®. Ursodiol (ursodeoxycholic acid, Actigall®) is a drug which helps bile flow more easily, may dissolve gall stones, and may have anti-inflammatory effects in the liver.
Elevated liver enzymes in dogs may not be serious, but should always be checked out.
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