Feline Liver Disease Guide: ALT/ALP/GGT/Bilirubin Interpretation + Lipidosis & Cholangitis

The Functions of a Cat's Liver

The liver is the largest solid organ in a cat's body. According to the Cornell Feline Health Center, its vital functions include helping digest food; storing and releasing energy as glycogen; synthesizing proteins and certain fats (triglycerides); storing vitamins; manufacturing bile, which is needed to absorb fats; and reducing the poisonous properties of toxic compounds.

Cats differ significantly from dogs in their hepatic detoxification mechanisms. Research published in Pharmacogenetics (Court & Greenblatt, 2000) has shown that cats lack certain Phase II detoxification enzymes (such as glucuronyl transferase), making many drugs and compounds that are safe for humans and dogs potentially toxic to cats. This is a critical reason why human medications should never be administered to cats without veterinary guidance.

Hepatic Lipidosis: A Common and Dangerous Feline Liver Disease

Feline hepatic lipidosis, commonly known as fatty liver disease, is a common liver condition in cats. In a 2024 study in the Journal of Veterinary Internal Medicine (Wallace et al.), about 60% of cats with hepatic lipidosis that received nutritional support survived, which is why early detection and early nutritional support matter so much.

Pathophysiology

When a cat stops eating or significantly reduces food intake for any reason, the body begins mobilizing peripheral fat stores for energy. However, the feline liver has limited capacity to process fatty acids efficiently. The influx of fatty acids overwhelms hepatic metabolism, leading to triglyceride accumulation within hepatocytes and a rapid decline in liver function.

High-Risk Groups

• Overweight cats: Obese cats are at significantly higher risk due to larger fat reserves
• Cats with sudden appetite loss: Just a few days without eating can trigger the condition
• Stressed cats: Moving, new household members, or environmental changes
• Middle-aged cats: In the 2024 study above, the median age at diagnosis was about 7 years

Clinical Signs

• Complete anorexia or markedly reduced appetite (lasting several days or more)
• Rapid weight loss
• Jaundice (yellowing of the skin, inner ears, gums, and sclera)
• Vomiting and lethargy
• Muscle wasting
• In severe cases, hepatic encephalopathy (behavioral changes, drooling, head pressing)

Treatment

The cornerstone of hepatic lipidosis treatment is aggressive nutritional support. Both the Merck Veterinary Manual and ISFM (International Society of Feline Medicine) guidelines favor an esophagostomy feeding tube. The energy target is the resting energy requirement (RER = 70 × body weight in kg to the 0.75 power), built up gradually from a small amount over a few days. Tube feeding usually lasts several weeks; ISFM suggests considering removal once the cat has eaten 75–100% of its RER on its own for 3–5 consecutive days.

Cholangitis and Cholangiohepatitis

Cholangitis is a common hepatobiliary disease in cats, characterized by inflammation of the biliary system. According to the WSAVA Liver Standardization Group, feline cholangitis is classified into three types: neutrophilic cholangitis, lymphocytic cholangitis, and chronic cholangitis associated with liver fluke infection. The two more common types are described below:

Neutrophilic Cholangitis

• Acute onset, closely associated with bacterial infection
• Bacteria typically ascend from the intestine via the bile duct (E. coli, Enterococcus, etc.)
• Signs: fever, abdominal pain, jaundice, vomiting, anorexia
• Treatment is primarily antibiotic therapy, usually for 4 to 6 weeks

Lymphocytic Cholangitis

• Chronic progression, potentially immune-mediated
• Higher incidence in Persian and Himalayan breeds
• Signs: recurrent appetite loss, weight loss, ascites
• Treatment may require immunosuppressive drugs (e.g., prednisolone)

Triaditis: When Cholangitis Comes With Company

Triaditis is not a type of cholangitis; the term describes cholangitis, pancreatitis and inflammatory bowel disease (IBD) occurring together. In a study in the Journal of Veterinary Internal Medicine (Fragkou et al., 2016), 8 of 27 cats with clinical signs (about 30%) had triaditis. The three organs are prone to becoming inflamed together because the feline bile duct and pancreatic duct merge before entering the duodenum, facilitating the spread of inflammation among these three organs.

Diagnostic Methods

Veterinarians use a combination of clinical findings and multiple diagnostic tests to evaluate liver disease:

According to Today's Veterinary Practice (McAtee & Lidbury), if liver enzymes stay elevated after causes outside the liver are ruled out, the usual next steps are bile acid testing and abdominal ultrasound, followed by biopsy when needed, to accurately differentiate between types of liver disease and guide appropriate treatment.

Feline Liver Enzyme Reference Table (ALT / ALP / GGT / Bilirubin)

When a blood biochemistry report flags "elevated liver enzymes," owners are often anxious but cannot interpret the numbers. Below are the four core feline liver markers with typical reference ranges, tissue source, and what an elevation means. Reference intervals vary substantially by lab and analyzer(different peer-reviewed studies report feline ALT upper limits anywhere from 83 to 120 U/L) — always use the reference range printed on your vet's lab report. The values below are for conceptual orientation only, not absolutes.

Reverse-engineering disease from enzyme pattern

Liver enzymes rarely elevate one at a time; specific patterns point to specific disease processes. Common patterns:

• ALT & AST markedly elevated, ALP/GGT milder →Hepatocellular damage pattern: acute liver toxicity (drugs, poisons), hepatitis, severe infection.
• ALP & GGT elevated together →Cholestasis pattern: strongly suspect cholangitis or bile duct obstruction; abdominal ultrasound needed.
• All four elevated + jaundice → Severe liver disease, possibly lipidosis, severe cholangitis, or liver tumor; hospitalization, supportive care, and biopsy typically required.
• Moderate ALT elevation + bilirubin elevation + ≥ 24 h anorexia → Strongly suspect hepatic lipidosis, one of the most dangerous feline liver diseases; requires urgent intervention.

Important reminder: elevated liver enzymes are a signal, not a diagnosis. The actual cause requires integration with clinical signs, imaging (abdominal ultrasound), liver function testing (bile acids or ammonia), and sometimes biopsy. Numbers alone don't make a diagnosis — discuss the report with your veterinarian.

Advanced liver function tests (beyond enzymes)

• Bile acids (SBA): assesses overall liver function. Sample paired pre-prandial (12 h fast) and 2 h post-prandial. Reference: pre-prandial 0–8 µmol/L, post-prandial 0–30 µmol/L. Sample handling is simple — the preferred initial functional test.
• Ammonia: reference fasting < 50 µg/dL. Requires heparinized tubes, ice transport, plasma separation within 30 minutes — logistically more challenging. Mainly used when portosystemic shunt (PSS) is suspected.
• SDMA, albumin, coagulation times (PT/aPTT): support assessment of liver synthetic function and systemic status.

High Liver Enzymes in Cats: What to Do, What to Feed, What to Avoid

If your cat's bloodwork shows elevated liver enzymes, don't rush to switch foods or buy supplements. Here is what the veterinary literature says about next steps and diet; your veterinarian's judgment comes first.

First: what happens next

• A higher number doesn't mean a worse outlook: Today's Veterinary Practice notes that the degree of liver enzyme elevation should not be used to indicate prognosis; it has to be read alongside symptoms and other tests.
• The cause may not be the liver: hyperthyroidism also raises ALT, so older cats usually have their thyroid hormone (T4) checked as well.
• Mild elevation in a cat that is eating and acting normally: your veterinarian may recheck in a few weeks. If values stay high, the next steps are bile acids, abdominal ultrasound and, if needed, biopsy.
• Above all, don't let your cat stop eating: ISFM guidelines recommend starting nutritional support no later than 3 days after a cat stops eating, counting the days already spent not eating at home.

See a veterinarian promptly if you notice (Merck Veterinary Manual): poor appetite, vomiting, jaundice (yellow whites of the eyes, gums or inner ears), a swollen belly or abnormal bleeding; or neurological signs such as drooling, dullness, head pressing, circling, blindness or seizures, which can mean liver failure is affecting the brain.

What to feed: don't switch to low protein on your own

• Most cats should not be protein-restricted: the Merck Veterinary Manual (Center) states that protein should be restricted only in specific situations such as hepatic encephalopathy, and that otherwise a protein-restricted prescription liver diet is inappropriate. In cats with hepatic lipidosis, protein restriction compromises survival.
• Easily digestible, palatable, calorie-dense food in small, frequent meals: fat usually does not need to be restricted either, with a few exceptions such as chronic bile duct obstruction that your veterinarian will assess.
• Act if your cat isn't eating enough: calorie targets are based on RER and increased gradually by your veterinarian. Appetite stimulants (such as mirtazapine) can only help so much; Merck notes they will not recover cats with severe hepatic lipidosis, which still need a feeding tube.
• Let your veterinarian decide on supplements: the evidence for SAMe, milk thistle (silybin), vitamin E and L-carnitine varies. For example, Merck notes that no oral milk thistle product is recognized to deliver therapeutic concentrations, and vitamin K1, used in jaundiced cats, can cause Heinz body anemia in cats if overdosed. None of these should be given on your own.

What to avoid

Rather than specific foods, the veterinary literature emphasizes avoiding the following:

• No fasting or crash diets: the Merck Veterinary Manual states that starvation is never a safe or humane way to cause weight loss. Losing weight too fast is itself a risk factor for hepatic lipidosis in obese cats.
• No human medications: acetaminophen (paracetamol) is extremely toxic to cats. Ask your veterinarian before giving any human medication or supplement.
• No essential oils around your cat: tea tree, birch tar, cinnamon and pennyroyal oils can cause liver failure in cats, because cats lack the enzyme needed to break these compounds down.
• "Low-fat, low-protein for the liver" is a myth: as explained above, these diets don't suit most cats with high liver enzymes. Onions and garlic are toxic to cats, but the main harm is anemia rather than liver damage; see the full list in foods cats can't eat.

Prevention and Dietary Management

Key measures for preventing feline liver disease include:

• Avoid prolonged fasting: This is the most important principle for preventing hepatic lipidosis. If a cat's appetite decreases for more than 48 hours for any reason, proactive intervention is necessary.
• Maintain a healthy weight: Weight loss in obese cats should be gradual, at about 0.5–2% of body weight per week (around 1% is a common target) to avoid triggering hepatic lipidosis.
• Provide high-quality protein: As obligate carnivores, cats require adequate animal-based protein to support normal liver metabolism. Choosing a diet that meets AAFCO nutritional standards for complete and balanced nutrition is essential.
• Regular health checkups: The AAHA/AAFP Feline Life Stage Guidelines recommend an exam at least once a year for all cats and at least every 6 months for senior cats over 10; the AAFP Senior Care Guidelines also recommend baseline lab testing at least yearly starting at 7–10 years of age.
• Keep liver-damaging substances away: human medications (especially acetaminophen) and essential oils (tea tree, birch tar, cinnamon, etc.). See "What to avoid" above.

For daily nutrition, providing moisture-rich food with high-quality protein supports healthy liver function. Complete Cat Food Cans (24-Pack) are formulated with premium animal protein, meet AAFCO complete and balanced nutrition standards, and feature high moisture content to support daily hydration.

References

1. McAtee, B.B. & Lidbury, J.A. Liver Enzyme Interpretation and Liver Function Tests. Today's Veterinary Practice (updated 2023). todaysveterinarypractice.com
2. Center, S.A. Feline Hepatic Lipidosis. Merck Veterinary Manual. merckvetmanual.com
3. Center, S.A. Nutrition in Hepatic Disease in Small Animals. Merck Veterinary Manual. merckvetmanual.com
4. Center, S.A. Disorders of the Liver and Gallbladder in Cats. Merck Veterinary Manual, Cat Owners Version. merckvetmanual.com
5. Center, S.A. Canine Cholangiohepatitis (section on oral silibinin products). Merck Veterinary Manual. merckvetmanual.com
6. Sanderson, S.L. Nutrition in Disease Management in Small Animals. Merck Veterinary Manual. merckvetmanual.com
7. Brooks, D., Churchill, J., Fein, K., et al. (2014). 2014 AAHA Weight Management Guidelines for Dogs and Cats. Journal of the American Animal Hospital Association, 50(1), 1-11. doi:10.5326/JAAHA-MS-6331
8. Benson, K. Toxicoses From Essential Oils in Animals. Merck Veterinary Manual. merckvetmanual.com
9. Wallace, O.P., Jablonski, S.A., Thomas, J.S., Bock, J.H. III & Langlois, D.K. (2024). Association of time to start of enteral nutrition and outcome in cats with hepatic lipidosis. Journal of Veterinary Internal Medicine, 38(6), 3144-3152. PMC11586538
10. Fragkou, F.C., Adamama-Moraitou, K.K., Poutahidis, T., et al. (2016). Prevalence and Clinicopathological Features of Triaditis in a Prospective Case Series of Symptomatic and Asymptomatic Cats. Journal of Veterinary Internal Medicine, 30(4), 1031-1045. PMC5089651
11. Court, M.H. & Greenblatt, D.J. (2000). Molecular genetic basis for deficient acetaminophen glucuronidation by cats: UGT1A6 is a pseudogene, and evidence for reduced diversity of expressed hepatic UGT1A isoforms. Pharmacogenetics, 10(4), 355-369. PubMed 10862526
12. WSAVA Liver Standardization Group (Rothuizen, J. et al.). (2006). WSAVA Standards for Clinical and Histological Diagnosis of Canine and Feline Liver Diseases. Saunders Elsevier.
13. Twedt, D.C. (2006). Update on Feline Hepatobiliary Disease. Journal of Feline Medicine and Surgery, 8(5), xi-xiv. PMC10822242
14. Cornell Feline Health Center. Hepatic Lipidosis. vet.cornell.edu
15. Cornell Feline Health Center. Cholangiohepatitis. vet.cornell.edu
16. Taylor, S. et al. (2022). 2022 ISFM Consensus Guidelines on Management of the Inappetent Hospitalised Cat. Journal of Feline Medicine and Surgery, 24(7), 614-640. PMC11107985
17. Quimby, J., Gowland, S., Carney, H.C., et al. (2021). 2021 AAHA/AAFP Feline Life Stage Guidelines. Journal of Feline Medicine and Surgery, 23(3), 211-233. PMC10812130
18. Ray, M., Carney, H.C., Boynton, B., et al. (2021). 2021 AAFP Feline Senior Care Guidelines. Journal of Feline Medicine and Surgery, 23(7), 613-638. PMC10812122