VetVaultHigh liver enzymes in cats: ALT, ALP, GGT and bilirubin explained
High liver enzymes in a cat mean liver cells or bile ducts are injured or stressed, not necessarily that the liver is failing. ALT rises when liver cells are damaged; ALP and GGT rise when bile flow is disturbed; bilirubin rises with liver disease, blocked bile ducts or red cell destruction. In cats even a mild ALP rise matters.
Cat liver values at a glance
Most chemistry panels include four liver values. Enzymes are reported in U/L (or IU/L), but their ranges vary widely between analyzers. For the rest of the panel, see our cat bloodwork guide.
| Test and what it measures | Approx. range | A high result can point to |
|---|---|---|
| ALT – enzyme inside liver cells that leaks out when they are damaged | 10–100 U/L | Liver cell injury: fatty liver (hepatic lipidosis), cholangitis, toxins, hyperthyroidism |
| ALP – enzyme on the bile side of liver cells, also made by bone | 10–80 U/L | Disturbed bile flow, hepatic lipidosis (often marked), hyperthyroidism, diabetes; growing kittens |
| GGT – enzyme of the bile ducts | 0–5 U/L | Bile duct inflammation (cholangitis), blocked bile flow, pancreatitis |
| Total bilirubin – yellow pigment from old red cells, cleared by the liver into bile | Under about 0.4 mg/dL (about 7 µmol/L) | Red cell destruction, liver disease, bile duct blockage |
Some panels also list AST, a leakage enzyme found in liver and muscle.
Always use the range on your own report. Ranges differ between laboratories and analyzers. The ranges here are approximate values for typical adult cats, meant only to help you orient yourself.
Call your vet promptly, or an emergency clinic if they are closed, whatever the blood results showed, if your cat:
- has eaten little or nothing for 24–48 hours – sooner if it is overweight, diabetic or already unwell;
- has yellow gums, whites of the eyes, ear flaps or skin (jaundice);
- vomits repeatedly;
- is lethargic, weak or hiding;
- has a swollen belly.
Do not wait for a cat that has stopped eating to "get hungry". In overweight cats especially, a few days without food can trigger fatty liver disease.
ALT, ALP and GGT: injury versus bile flow
Liver enzymes mark damage or disturbed bile flow, not liver function. A cat with long-standing liver disease can even have normal enzymes if no active injury is happening, so vets read them with the function clues described below.
ALT: a leakage enzyme
ALT sits inside liver cells and leaks into the blood when they are injured. In cats it is fairly specific to the liver and appears to clear from the blood within hours, so a raised ALT usually reflects recent or ongoing injury. A rise of 2–3 times the upper limit is often called mild and more than 10 times marked, but size alone does not show how well the liver works or whether it will recover. Cats' red cells also contain ALT, so a hemolysed sample (burst red cells) can nudge it up.
ALP and GGT: cholestatic, induced enzymes
Rather than simply leaking out, ALP and GGT are produced in larger amounts when bile flow is slowed or blocked (cholestasis). ALP is also made by bone; GGT is concentrated in the cells lining the bile ducts.
Why a mild ALP rise matters more in cats than in dogs
- Little ALP to start with. Feline liver cells contain much less ALP than canine ones.
- Short half-life. Liver ALP lasts about 6 hours in a cat's blood, versus days in a dog's, so a raised value means it is still being produced.
- No steroid-induced ALP. Dogs make an extra ALP isoenzyme in response to steroids; cats do not, so steroids rarely explain a high ALP in a cat.
The main exceptions are growing kittens and hyperthyroid cats, in which much of the extra ALP comes from bone.
Reading ALP and GGT together
In hepatic lipidosis, ALP often rises markedly while GGT stays normal or only mildly raised. In cholangitis, bile duct obstruction and pancreatitis, GGT tends to rise more, sometimes more than ALP. Treat this as a tendency, not a rule: fatty liver triggered by pancreatitis or cholangitis can raise both. Vets use the pattern to guide next tests, not to diagnose.
Bilirubin and jaundice
Bilirubin is made when old red cells are broken down; the liver clears it into the bile. It rises for three broad reasons:
- Before the liver (pre-hepatic) – red cells destroyed faster than normal, for example by the blood parasite Mycoplasma haemofelis, immune-mediated anemia or onion or paracetamol (acetaminophen) toxicity. The clue is anemia on the blood count.
- In the liver (hepatic) – hepatic lipidosis, cholangitis, feline infectious peritonitis (FIP) or tumours.
- After the liver (post-hepatic) – a blocked bile duct from pancreatitis, gallstones, thick bile or a tumour.
Jaundice (yellow gums, eyes, ear flaps or skin) usually appears only once bilirubin is well above the range. Unlike in dogs, bilirubin in a cat's urine is usually abnormal. High bilirubin alone does not mean liver failure; jaundiced cats with fatty liver often recover with treatment.
Liver function clues: albumin, glucose, cholesterol, BUN and bile acids
The liver makes albumin, glucose, cholesterol and clotting factors and turns ammonia into urea, so a major loss of function can change these values. None is specific on its own.
| Value | What it can say about the liver | Other common reasons it changes |
|---|---|---|
| Albumin | Low with long-standing loss of liver function | Low with protein loss through gut or kidneys, inflammation or poor nutrition; high with dehydration |
| Glucose | Low with severe liver failure or a portosystemic shunt (an abnormal vessel that bypasses the liver) | High with stress at the clinic or diabetes |
| Cholesterol | Low with reduced liver function or a shunt; high when bile flow is blocked | High with diabetes or after a meal |
| BUN / urea | Low when the liver makes less urea, as with liver failure or a shunt | Low with a low-protein diet or heavy drinking; high with dehydration or kidney disease (see cat kidney values) |
| Bile acids | A true function test: high when the liver cannot clear them or blood bypasses the liver | Not useful once bilirubin is high or the cat is jaundiced, because blocked bile flow raises them anyway |
Bile acids are usually measured as a pair: fasting and about 2 hours after a small meal. Results above roughly 25 µmol/L are generally taken to suggest liver disease or abnormal liver blood flow, but use your lab's cut-off.
Common causes of raised liver values in cats
| Cause | Typical blood pattern | Notes |
|---|---|---|
| Hepatic lipidosis (fatty liver) | Marked ALP rise; GGT normal or mildly raised; ALT raised; high bilirubin; often low potassium | Often after an overweight cat stops eating; usually triggered by another illness or stress |
| Cholangitis / cholangiohepatitis | Raised ALT, ALP and GGT, with GGT often relatively higher; bilirubin may be raised | Neutrophilic (usually bacterial) or lymphocytic (immune-related). Often occurs with pancreatitis and inflammatory bowel disease ("triaditis") |
| Hyperthyroidism | ALT and ALP often mildly raised; GGT and bilirubin usually normal; high T4 | Older cats losing weight despite a good appetite; enzymes often fall once thyroid levels are controlled. See our cat thyroid T4 guide |
| Diabetes mellitus | ALT and ALP often mildly raised; high glucose and fructosamine | A diabetic cat that stops eating can also develop hepatic lipidosis |
| Toxins and some medications | Often a sharp ALT rise; bilirubin may rise | Cats lack some liver pathways for breaking down drugs and toxins. Never give a cat human painkillers such as paracetamol |
| Infections, including FIP | FIP: high bilirubin, often with only mild enzyme changes, and high globulin | Toxoplasmosis can also raise liver values |
| Tumours | Anything from normal to markedly raised | Lymphoma, bile duct tumours or spread from elsewhere |
| Extrahepatic bile duct obstruction | High GGT, ALP and bilirubin | Blockage outside the liver from pancreatitis, gallstones, thick bile or a tumour |
| Red cell destruction (not a liver disease) | High bilirubin with anemia; enzymes normal or mildly raised | Blood parasites, immune-mediated anemia, onion or paracetamol toxicity |
If your cat takes any medication, ask your vet whether it could be involved, and do not stop or change a medicine without their advice.
Hepatic lipidosis: why a cat that stops eating is urgent
Hepatic lipidosis is one of the most common serious liver diseases in cats, and the one owners can most influence. When a cat stops eating, its body moves stored fat to the liver faster than the liver can process it. Fat builds up inside liver cells, the cells swell, bile flow slows and the liver begins to fail.
Overweight cats are at the highest risk. Most cases follow another problem that put the cat off its food: pancreatitis, cholangitis, diabetes, kidney disease, hyperthyroidism, cancer, or stress such as a house move, boarding or a new food the cat refuses. Rapid weight loss is risky too, so weight-loss plans should be gradual and vet-guided.
Signs include avoiding the food bowl, sometimes drooling at food, hiding, vomiting, weight loss and, later, jaundice. The classic blood picture is a marked ALP rise with a normal or only mildly raised GGT, plus raised ALT and bilirubin.
Without prompt treatment hepatic lipidosis is often fatal, but many cats recover with early, intensive nutrition: usually a feeding tube, fluids, correction of potassium and other electrolytes, and treatment of the underlying cause. Tube feeding often continues at home for several weeks. Cats that recover rarely relapse.
The key takeaway: a cat that has not eaten for more than a day or two, especially an overweight cat, needs a vet promptly, even if it seems otherwise fine.
What vets usually do next
Next steps depend on how unwell your cat is and how high the values are:
- Repeat the panel. A single mild rise in a well cat is often rechecked after a few weeks to see the trend.
- T4 in older cats. Hyperthyroidism is a common, treatable reason for raised ALT and ALP.
- Urinalysis. Bilirubin or glucose in the urine adds clues.
- Bile acids. To test liver function when the cat is not jaundiced.
- Abdominal ultrasound. Shows the liver, gallbladder, bile ducts, pancreas, intestines and any masses.
- Fine-needle aspirate. A thin needle, usually guided by ultrasound, collects liver cells; often enough to confirm hepatic lipidosis. Clotting is usually checked first.
- Biopsy or bile sample. Needed to confirm and classify cholangitis and many tumours.
- Other tests. A pancreas-specific lipase test for pancreatitis, or tests for FIP and other infections.
Questions to ask your vet
- Which liver values are raised, and by roughly how much?
- Does the pattern suggest liver cell injury, bile flow problems or red cell destruction?
- Could hyperthyroidism, diabetes, a medication or the sample itself explain it?
- Do we need bile acids, an ultrasound or a T4 test, and when should we recheck?
- How much should my cat eat, and what should I do if it eats less?
- Can I have a copy of the full report with reference ranges?
Frequently asked questions
What does high ALT mean in a cat?
ALT is an enzyme inside liver cells that leaks into the blood when those cells are damaged. In cats it commonly rises with fatty liver (hepatic lipidosis), inflammation of the liver and bile ducts (cholangitis), toxins and hyperthyroidism. It shows injury, not how well the liver works, so vets read it with ALP, GGT, bilirubin and the cat's symptoms.
Is a mildly high ALP serious in a cat?
It deserves attention. Cats have little ALP in their liver cells, clear it from the blood within hours and, unlike dogs, do not make extra ALP in response to steroids, so even a mild rise is more meaningful than in a dog. Growing kittens and hyperthyroid cats are common exceptions, because some of their ALP comes from bone.
What does high GGT mean in a cat?
GGT is an enzyme of the bile ducts. A raised GGT in a cat points towards bile duct inflammation (cholangitis), blocked bile flow or pancreatitis affecting the bile duct. In fatty liver, GGT tends to stay normal or only mildly raised even when ALP is high, although this is a tendency rather than a rule.
What causes high bilirubin in a cat?
Bilirubin can rise because red cells are being destroyed faster than normal, because the liver is diseased, or because the bile duct is blocked. Yellow gums, skin or eyes (jaundice) usually appear once bilirubin is well above the range. Any cat with jaundice should see a vet promptly.
What blood work is typical of hepatic lipidosis in cats?
Typically a marked rise in ALP with a normal or only mildly raised GGT, raised ALT, high bilirubin and often low potassium. GGT can be higher when an inflammatory disease such as pancreatitis or cholangitis triggered the fatty liver. Vets confirm it with ultrasound and a fine-needle aspirate of the liver.
How long can a cat go without eating before it risks fatty liver?
There is no safe fixed limit. A cat that has eaten little or nothing for more than a day or two should be seen by a vet, and sooner if it is overweight, diabetic or already unwell, because overweight cats that stop eating are at particular risk of hepatic lipidosis.
Can hyperthyroidism cause high liver enzymes in cats?
Yes. Hyperthyroidism commonly raises ALT and ALP, usually mildly, while GGT and bilirubin tend to stay normal. Much of the extra ALP comes from bone. The enzymes often fall once thyroid levels are controlled, which is why vets check T4 in older cats with raised liver values.
Can high liver enzymes in a cat go back to normal?
Often, yes, if the cause is found and treated. The liver has a large capacity to regenerate, and enzymes commonly settle after recovery from fatty liver or once hyperthyroidism is controlled. Your vet will usually recheck the panel to confirm the trend.
Sources
- eClinPath, Cornell University College of Veterinary Medicine. Liver (liver injury, cholestasis, bilirubin and liver function tests). eclinpath.com/chemistry/liver
- eClinPath, Cornell University College of Veterinary Medicine. Alkaline phosphatase. eclinpath.com/chemistry/liver/cholestasis/alkaline-phosphatase
- Cornell Feline Health Center. Hepatic Lipidosis. vet.cornell.edu
- Cornell Feline Health Center. Cholangiohepatitis. vet.cornell.edu
- Merck Veterinary Manual. Feline Hepatic Lipidosis. merckvetmanual.com
- International Cat Care. Liver and gall bladder disease in cats. icatcare.org