Elevated Liver Enzymes in Dogs: What High ALT and ALP Mean

A high liver enzyme on your dog's blood test tells your veterinarian that liver cells are damaged or that bile is not flowing normally. It does not tell anyone why, and often the cause isn't in the liver at all. Internal medicine specialist Dr. David Twedt notes that the most common cause of abnormal liver enzymes is not primary liver disease. It is the liver reacting to a problem somewhere else in the body, or to a medicine.

So one high number is a clue, not a diagnosis. What your vet does with it depends on which values are high, how high they are, whether they stay high, and whether your dog is sick. If your dog has yellow gums or eyes, is vomiting and not eating, or seems confused, go straight to "When to Call Your Vet Now" below.

What ALT, ALP, AST, GGT and Bilirubin Mean

Liver values fall into two groups. ALT and AST are "leakage" enzymes: they sit inside liver cells and spill into the blood when those cells are injured. ALP and GGT are "induction" enzymes: the liver makes more of them when bile flow slows down (vets call this cholestasis) or when certain drugs switch production on. Bilirubin is a yellow pigment the liver clears into bile.

A few details the table can't hold:

• ALT is found mostly in the liver, with smaller amounts in muscle, kidney and red blood cells (Cornell University's eClinPath). After a sudden injury it peaks at about two days and can take days to weeks to fall, one reason vets recheck rather than react to one result.
• AST is high in muscle too, so high AST with a normal ALT points to muscle or red blood cells first.
• ALP causes the most confusion, because dogs make a form of it that steroids switch on, including, per Royal Canin's clinical pathology review, steroid creams. But in an adult dog without bone disease, a raised ALP usually comes from the liver and bile system, and Twedt is clear that abnormal liver enzymes should not be ignored.
• GGT is high in only about half of dogs with liver or bile disease in the figures Twedt cites, so a normal GGT does not rule liver disease out. It is more specific (about 87%), and when ALP and GGT are both high, specificity for liver and bile disease rises to about 94%. Seizure medicines raise ALP but not GGT, which helps separate a drug effect from bile duct disease.
• Bilirubin comes from old red blood cells. High enough, it shows as jaundice: yellow gums, eyes or skin.

How High Is Too High?

Start with the range printed beside each value. Each lab and analyzer sets its own reference interval from healthy adult dogs, and by design it covers the middle 95% of them (eClinPath). So about 1 healthy dog in 20 lands just outside the range on any given test. Only your own lab's ranges apply to your dog.

Size matters too. Clinical pathologists often call a rise of 2 to 3 times the upper limit mild, 4 to 5 times moderate and more than 10 times marked, though clinicians draw these lines differently. For ALT, Twedt's rule of thumb is that more than twice the upper limit, or any rise that stays abnormal over weeks to months, deserves a closer look.

Two more things shape how a vet reads the numbers:

• The trend matters more than one result. An unexplained ALT increase lasting more than two months is the best screening clue for chronic hepatitis, according to the ACVIM consensus statement on chronic hepatitis in dogs.
• Normal enzymes do not prove a healthy liver. A dog with a liver shunt, advanced scarring (cirrhosis) or some liver tumors can have normal or only mildly raised enzymes. That is why vets also look at liver function values such as albumin, glucose, urea (BUN), cholesterol, bilirubin and clotting times.

Liver Causes of High Liver Enzymes

These start in the liver or its bile system (vets say "hepatic").

• Chronic hepatitis. Long-term liver inflammation that can stay silent: up to 20% of affected dogs have raised enzymes without any illness (ACVIM). Predisposed breeds include Bedlington Terriers, Doberman Pinschers, Labrador Retrievers, Dalmatians and Cocker Spaniels, and copper building up in the liver is the most common known cause.
• Toxins and drug reactions. Xylitol, acetaminophen, sago palms, Amanita mushrooms, blue-green algae, moldy food (aflatoxins) and some rodent poisons can all injure a dog's liver (Merck Veterinary Manual). Some prescribed drugs can too, even at the correct dose.
• Infections. Leptospirosis, a bacterial infection that can also infect people, and infectious canine hepatitis, caused by canine adenovirus 1.
• Portosystemic shunts. An abnormal vessel carries blood from the gut around the liver instead of through it. Congenital portosystemic shunts are seen in breeds such as Yorkshire Terriers, Maltese, Miniature Schnauzers and Irish Wolfhounds (American College of Veterinary Surgeons). Enzymes may be only mildly raised while bile acids are usually very high.
• Gallbladder and bile duct disease. A gallbladder mucocele (thick, jelly-like mucus filling the gallbladder), gallstones or a bile duct blocked by pancreatitis can push ALP and GGT up. Shetland Sheepdogs are predisposed to mucoceles, and the signs are often vague until the gallbladder blocks or ruptures.
• Liver tumors. Mostly found in dogs over 9 years old; cancer that has spread to the liver from elsewhere is more common than tumors that start there.
• Trauma such as being hit by a car often raises ALT.
• Nodular hyperplasia. Benign, age-related nodules, common in older dogs, that can look like more serious disease on ultrasound.

Non-Liver Causes of High Liver Enzymes

Here the liver is reacting to a problem that starts somewhere else ("extrahepatic"), and the values usually settle once that problem is treated.

• Steroids and seizure medicines. Steroid tablets, injections and even creams can raise ALP, and sometimes GGT and ALT; phenobarbital often raises ALP. Tell your vet about any recent steroid, even an ointment for the skin or ears.
• Cushing's disease. A common hormone disease of adult and older dogs. High ALP is one of its most typical lab findings.
• Growth and bone. Puppy ALP usually reaches the adult range by about 15 months of age. In adults, some bone diseases, including bone cancer (osteosarcoma), can raise ALP.
• Red blood cell destruction and muscle injury. Hemolytic anemia raises bilirubin and can raise AST, and so can a sample that hemolyzed in the tube. Muscle injury raises AST more than ALT.
• Illness in other organs. Pancreatitis, gut disease, sepsis, low oxygen from heart disease or severe anemia, diabetes and hypothyroidism can all raise liver values.

Three breeds are worth knowing about. Some Siberian Huskies have a harmless inherited high ALP from bone. In Scottish Terriers, high ALP is common and often tied to adrenal-related liver changes that can progress, so it is not "just the breed". And in a study of 105 healthy Miniature Schnauzers, those with moderately to severely high blood fats (triglycerides) were far more likely to have high ALP, which makes the blood fats worth investigating rather than a reason to dismiss the result.

What Tests Come Next?

Your vet will start by asking about medicines (including creams and ear or eye drops), possible toxins, diet and any changes at home, and by examining your dog.

If your dog seems well and the rise is mild, a common approach is to repeat the test after a few weeks while looking for non-liver causes, then move to liver function tests and an ultrasound if it is still high (Twedt). If your dog is sick or the values are very high, testing moves faster and runs in parallel.

The tests you are most likely to hear about:

1. Chemistry panel, blood count and urinalysis. High ALT and AST point to liver cell injury; high ALP, GGT and bilirubin point to a bile-flow problem. Liver disease can change red cell shape, for example with more "target cells" (VCA Animal Hospitals), and urine can show ammonium biurate crystals, a clue to liver disease or a shunt. Low albumin, glucose or urea suggest the liver is struggling to do its job.
2. Bile acids. A liver function test, usually one sample after a fast and a second about two hours after a meal. High results suggest the liver is not working well or that blood is bypassing it, as with a shunt. It does not name the disease.
3. Abdominal ultrasound. The most useful first imaging test for the liver and gallbladder: size, texture, masses, gallstones, a mucocele and some shunts. A normal-looking liver does not rule out early chronic hepatitis (ACVIM).
4. Clotting tests, because the liver makes clotting proteins and vets check clotting before a biopsy.
5. Liver samples. A fine-needle aspirate can help, but a liver biopsy is needed for a definite diagnosis of most liver diseases, including chronic hepatitis.
6. Tests for the suspected cause, such as adrenal tests for Cushing's disease, a leptospirosis test, or a CT scan when a shunt is suspected.

When to Call Your Vet Now

Call your veterinarian or an emergency clinic now if your dog has a high liver value, or might have liver trouble, and you see any of these:

• Yellow gums, whites of the eyes or skin (jaundice)
• Vomiting together with not eating, or vomiting again and again
• Confusion, wandering, pressing the head against walls, sudden blindness, drooling or seizures, which can mean toxins the liver should clear are reaching the brain (hepatic encephalopathy)
• A swollen belly from fluid (ascites)
• Unusual bleeding or bruising, collapse or sudden weakness
• Your dog ate, or might have eaten, xylitol, a human pain reliever, sago palm, wild mushrooms or anything else toxic, or swam in water with blue-green algae scum. Do not wait for signs: with xylitol, liver enzymes often rise within hours, while signs of liver injury may not appear for a day or two (Merck Veterinary Manual)

See your vet soon, within a day or two, if your dog is eating less, has mild vomiting or diarrhea, is drinking and peeing more, is losing weight, or seems tired. These signs are not specific to the liver, but with a high liver value they need a plan.

If your dog is bright and well and the high value turned up on routine bloodwork, agree on the next step with your clinic and mention any new medicine, cream or ear drops at the recheck. Catching liver changes before signs appear is the whole point of screening.

Treatment Depends on the Cause

There is no single treatment for "high liver enzymes". Your veterinarian treats the cause and uses the enzymes to track progress. A non-liver cause such as Cushing's disease, pancreatitis or hypothyroidism is treated first, and the liver values usually improve as it comes under control. A medicine effect is weighed against what the medicine does for your dog, so do not stop a prescribed steroid or seizure medicine because of a liver value; ask your vet first.

Some problems need surgery, for example many congenital shunts, most gallbladder mucoceles, and a liver tumor confined to one lobe. Chronic hepatitis is managed long term with a plan built on biopsy results, such as lowering liver copper when copper is the cause.

Ask your vet before giving any liver supplement or changing your dog's diet. Neither replaces finding the cause.

If your dog's bloodwork shows high liver enzymes, don't panic. Ask your vet two questions: could a medicine or another illness explain this, and what is the next test or recheck? The liver has a large reserve and a real ability to regenerate, which is good news for the many dogs whose cause is found and treated.

Originally written by Helen Roberts. Updated by the I Love Veterinary editorial team.

Sources

• Twedt DC. Why Are Liver Enzymes Increased? WSAVA World Congress Proceedings, 2014 (VIN)
• Webster CRL et al. ACVIM consensus statement on the diagnosis and treatment of chronic hepatitis in dogs. J Vet Intern Med, 2019
• Cornell University eClinPath: Alanine aminotransferase
• Cornell University eClinPath: Aspartate aminotransferase
• Cornell University eClinPath: Alkaline phosphatase
• Cornell University eClinPath: Gamma-glutamyl transferase
• Cornell University eClinPath: Bilirubin
• Cornell University eClinPath: Bile acids
• Cornell University eClinPath: Reference intervals
• Merck Veterinary Manual: Disorders of the Liver and Gallbladder in Dogs
• Merck Veterinary Manual: Xylitol Toxicosis in Dogs
• Merck Veterinary Manual: Disorders of the Adrenal Glands in Dogs
• American College of Veterinary Surgeons: Portosystemic Shunts
• American College of Veterinary Surgeons: Gallbladder Mucocele
• Klenner-Gastreich S. Canine liver enzymes: FAQs. Royal Canin Academy
• Xenoulis PG et al. Serum liver enzyme activities in healthy Miniature Schnauzers with and without hypertriglyceridemia. JAVMA, 2008
• VCA Animal Hospitals: Testing for Liver Disease

This article is for general information and is not a substitute for advice from your veterinarian.