ALT (alanine aminotransferase) is a liver enzyme found inside liver cells. When liver cells are damaged, ALT leaks into the bloodstream. Normal range: 10-120 U/L (varies by lab). ALT is highly liver-specific in cats and a reliable marker for liver cell damage.

What does high ALT mean in cats?

High ALT (over 120 U/L) indicates liver cell damage. Common causes in cats include hepatic lipidosis (fatty liver), hyperthyroidism, cholangiohepatitis, diabetes, and toxin exposure. Severity depends on how high the level is and whether other liver values are also abnormal.

What is normal ALT range for cats?

Normal ALT range for cats is typically 10-120 U/L, though this varies by laboratory. ALT 121-360 U/L is mildly elevated (2-3x normal). ALT 361-600 U/L is moderately elevated (3-5x normal). ALT over 600 U/L is severely elevated and needs urgent attention.

What causes high ALT in cats?

Common causes of high ALT in cats include: hepatic lipidosis (fatty liver from not eating), hyperthyroidism, cholangiohepatitis, diabetes, toxins (lilies, certain medications), infections (FIP, FeLV), pancreatitis, and cancer. Hepatic lipidosis is especially common and dangerous in cats.

When should I worry about ALT in cats?

Worry when: ALT is over 600 U/L (severe, needs urgent care), your cat has stopped eating for more than 24-48 hours (risk of hepatic lipidosis), your cat shows symptoms (jaundice, vomiting, lethargy), or ALT is elevated with high bilirubin or ALP. Cats that stop eating can develop fatty liver rapidly.

What is hepatic lipidosis in cats?

Hepatic lipidosis (fatty liver disease) occurs when a cat stops eating and the body mobilizes fat to the liver faster than it can process. This is unique to cats and can be life-threatening within days. It causes very high ALT and requires immediate veterinary care with aggressive nutritional support.

ALT in Cats: Normal Range, What High Levels Mean & When to Worry

Q: Is high ALT always serious in cats?

Not always. Mild elevations (up to 2x normal) can be from stress, minor illness, or medications. However, cats are more vulnerable than dogs to certain liver conditions like hepatic lipidosis, so elevated ALT should always be investigated, especially if your cat isn't eating well.

Q: How do you lower ALT in cats?

Treatment focuses on the underlying cause: treating hyperthyroidism, managing diabetes, aggressive feeding support for hepatic lipidosis, or treating infections. Liver supplements like SAMe and milk thistle may help. The most critical factor is ensuring your cat continues eating.

Quick Answer: Normal ALT in Cats

Normal ALT range: 10-120 U/L. High ALT indicates liver cell damage or stress. In cats, common causes include hepatic lipidosis (fatty liver), hyperthyroidism, and cholangiohepatitis.

If your cat's bloodwork shows a high ALT value, this guide explains what it means, why it rises, and what steps to take next. Cats have some unique liver conditions that require prompt attention.

What is ALT in Cats?

ALT (Alanine Aminotransferase) is an enzyme found inside liver cells. When liver cells are damaged or stressed, ALT leaks into the bloodstream, causing levels to rise on blood tests.

ALT is highly liver-specific in cats, making it a reliable marker for liver cell damage. However, the degree of elevation, trends over time, and your cat's symptoms all matter when interpreting results. Cats can develop serious liver conditions quickly, so elevated ALT warrants attention.

ALT Severity Chart: Understanding Your Cat's Results

10-120 U/L

Normal

Meaning: Liver enzymes within healthy range

Action: Routine monitoring as part of wellness exams

121-360 U/L

Mild

Meaning: Often stress-related, hyperthyroidism, or minor illness (2-3x normal)

Action: Recheck in 2-4 weeks, check thyroid levels, ensure cat is eating

361-600 U/L

Moderate

Meaning: Significant liver stress, possible cholangiohepatitis or early hepatic lipidosis (3-5x normal)

Action: Additional testing (ultrasound, bile acids), ensure nutritional intake

601-1200 U/L

Severe

Meaning: Serious liver damage, hepatic lipidosis, toxin exposure, or acute hepatitis (5-10x normal)

Action: Immediate workup, aggressive treatment, likely hospitalization

>1200 U/L

Critical

Meaning: Acute liver failure, severe hepatic lipidosis, or massive toxin exposure (>10x normal)

Action: Emergency care, IV fluids, nutritional support, intensive monitoring

ALT Level (U/L)	Severity	What It Means	Typical Action
10-120	Normal	Liver enzymes within healthy range	Routine monitoring as part of wellness exams
121-360	Mild	Often stress-related, hyperthyroidism, or minor illness (2-3x normal)	Recheck in 2-4 weeks, check thyroid levels, ensure cat is eating
361-600	Moderate	Significant liver stress, possible cholangiohepatitis or early hepatic lipidosis (3-5x normal)	Additional testing (ultrasound, bile acids), ensure nutritional intake
601-1200	Severe	Serious liver damage, hepatic lipidosis, toxin exposure, or acute hepatitis (5-10x normal)	Immediate workup, aggressive treatment, likely hospitalization
>1200	Critical	Acute liver failure, severe hepatic lipidosis, or massive toxin exposure (>10x normal)	Emergency care, IV fluids, nutritional support, intensive monitoring

While mild elevations may resolve with monitoring, moderate-to-severe elevations require prompt investigation. Unlike dogs, cats can develop life-threatening hepatic lipidosis within days if they stop eating — making early intervention critical.

Cat ALT Over 600 or 1200 — When to Worry

ALT over 600 U/L (5-10x normal) indicates significant liver cell damage requiring immediate diagnostics. In cats, this often points to hepatic lipidosis, acute cholangiohepatitis, or toxin exposure. Your vet will likely recommend hospitalization, IV fluids, and nutritional support.

ALT over 1200 U/L (>10x normal) is a liver emergency. Common causes include severe hepatic lipidosis, toxin ingestion (lilies are extremely dangerous to cats), or acute liver failure. Intensive care with aggressive feeding support is typically required.

Remember: ALT levels must be interpreted alongside your cat's symptoms, eating habits, and other bloodwork. A cat with moderately elevated ALT who is eating normally is less urgent than a cat with mild elevation who hasn't eaten in 48 hours.

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Common Causes of High ALT in Cats

Hepatic Lipidosis (Fatty Liver): Unique to cats — occurs when cats stop eating and fat overwhelms the liver. Life-threatening without treatment.
Hyperthyroidism: Very common in older cats. The overactive thyroid stresses the liver, causing mild-to-moderate ALT elevation.
Cholangiohepatitis: Inflammation of the bile ducts and liver tissue. Often occurs with pancreatitis and inflammatory bowel disease (triaditis).
Diabetes: Uncontrolled diabetes can affect liver function and elevate ALT.
Toxins: Lilies (extremely toxic to cats), certain medications, plants, and chemicals.
Infections: Feline Infectious Peritonitis (FIP), FeLV, FIV, bacterial infections.
Cancer: Lymphoma is the most common liver cancer in cats.

Hepatic Lipidosis: A Cat-Specific Emergency

Hepatic lipidosis deserves special attention because it's unique to cats and can develop rapidly. When a cat stops eating — for any reason — the body mobilizes fat stores for energy. In cats, this fat floods the liver faster than it can be processed, causing liver failure.

Any cat that stops eating for more than 24-48 hours is at risk. Overweight cats are especially vulnerable. Early signs include lethargy, hiding, and yellow discoloration of the ears or gums. Treatment requires aggressive nutritional support, often via feeding tube, and has a good prognosis if caught early.

Breed Predispositions

Some cat breeds have higher risk for certain liver conditions:

• Siamese — Hepatic amyloidosis (abnormal protein deposits in liver)
• Abyssinian — Hepatic amyloidosis
• Persian & Himalayan — Various liver conditions
• Any overweight cat — Increased risk of hepatic lipidosis

However, hepatic lipidosis can affect any cat of any breed — the key risk factor is not eating.

Symptoms Pet Owners Might Notice

Cats with elevated ALT may show:

• Loss of appetite (critical warning sign in cats)
• Lethargy or hiding
• Vomiting or diarrhea
• Weight loss
• Yellow discoloration of eyes, gums, or ear flaps (jaundice)
• Increased thirst and urination
• Drooling (especially with nausea)

Note: Cats are masters at hiding illness. A cat with elevated ALT may appear normal until the condition is advanced. Never ignore appetite changes.

What Happens Next?

Your veterinarian may recommend:

• Thyroid testing (T4) — Hyperthyroidism is extremely common in older cats
• Additional liver tests (bile acids, GGT, bilirubin)
• Abdominal ultrasound to visualize liver structure
• Rechecking bloodwork in 2-4 weeks
• FeLV/FIV testing if not recently done
• Nutritional support — ensuring your cat eats is critical
• Liver supplements like SAMe or milk thistle

Key Takeaway

High ALT indicates liver cell stress — but the most important factor in cats is whether they're eating.

A cat with mildly elevated ALT who is eating well can often be monitored. A cat with any ALT elevation who isn't eating needs immediate attention to prevent hepatic lipidosis.

Monitor Your Cat's ALT Trends

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✓ What your cat's specific ALT level means
✓ Whether other values suggest hepatic lipidosis risk
✓ How thyroid and liver values connect
✓ Questions to ask your vet at the next visit

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Frequently Asked Questions

Is high ALT always serious in cats?

Not always. Mild elevations can be from stress, minor illness, or hyperthyroidism. However, cats are vulnerable to hepatic lipidosis, so any ALT elevation combined with decreased appetite warrants attention.

What is hepatic lipidosis?

Hepatic lipidosis (fatty liver disease) is a life-threatening condition unique to cats. It occurs when a cat stops eating and fat overwhelms the liver. Treatment requires aggressive nutritional support, often via feeding tube.

Can hyperthyroidism cause high ALT?

Yes. Hyperthyroidism is very common in older cats and often causes mild-to-moderate ALT elevation. The increased metabolic rate stresses the liver. ALT typically improves once hyperthyroidism is treated.

What is a normal ALT level in cats?

Normal ranges are typically 10-120 U/L, though this varies by laboratory and testing method.

How do you lower ALT in cats?

Treatment focuses on addressing the underlying cause: treating hyperthyroidism, managing diabetes, aggressive feeding support for hepatic lipidosis, or treating infections. The most critical factor is ensuring your cat continues eating.

Can ALT levels go back to normal?

Yes, in many cases. If the cause is treatable (hyperthyroidism, infection, temporary stress), ALT often normalizes within weeks. Even hepatic lipidosis can resolve with aggressive nutritional support.

How long can a cat go without eating before hepatic lipidosis develops?

Hepatic lipidosis can begin developing in as little as 2-3 days without food, especially in overweight cats. Any cat that hasn't eaten for 24-48 hours should be evaluated by a vet.

What other tests are done with ALT?

Vets typically check ALP, GGT, and bilirubin (other liver markers), plus T4 (thyroid) since hyperthyroidism is so common in older cats. Bile acids test liver function. Ultrasound helps visualize liver structure.

Are lilies really that dangerous to cats?

Yes. All parts of true lilies (Easter lily, tiger lily, Asiatic lily, etc.) are extremely toxic to cats and can cause acute kidney failure and liver damage. Even small exposures can be fatal. If your cat has any contact with lilies, seek emergency care immediately.

Which cat breeds are prone to liver problems?

Siamese and Abyssinian cats are predisposed to hepatic amyloidosis. Persian and Himalayan cats may have increased risk of certain liver conditions. However, hepatic lipidosis can affect any cat that stops eating.