Cat Liver Enzymes Explained: ALT, ALP, AST, GGT Normal Ranges & Meaning

Liver enzymes are one of the most common abnormalities on cat bloodwork—especially in seniors. Unlike dogs, cats rarely have "benign" enzyme elevations, so any significant increase warrants attention. This comprehensive guide explains what each enzyme means, how they work together, and when to worry.

Looking for ALT-specific information? See our detailed guide: ALT in Cats: Normal Range, What High Levels Mean & When to Worry

What Are Liver Enzymes?

The liver is your cat's metabolic powerhouse, supporting digestion, detoxification, and protein production. When liver cells are stressed or damaged, enzymes leak into the bloodstream. The four main liver enzymes tested are:

• • ALT — The most liver-specific enzyme. Elevated ALT almost always means liver cell damage. See our ALT guide for details.
• • ALP — Rises with bile duct problems or bone disease. In cats, any ALP elevation is significant. See our ALP guide for details.
• • AST — Found in liver AND muscle. High AST with normal ALT usually means muscle injury, not liver disease. See our AST guide for details.
• • GGT — Specific to bile ducts. When elevated with ALP, strongly suggests cholangitis or obstruction. See our GGT guide for details.

Normal Liver Enzyme Ranges for Cats

Ranges vary slightly between labs. Your vet interprets results in context of your cat's history and symptoms.

Most Common Causes by Pattern

Vets look at which enzymes are elevated together to narrow down the cause:

• ALT elevated alone: Hepatic lipidosis (fatty liver) is the #1 cause in cats who stopped eating. Also consider toxin exposure, infections, or hyperthyroidism.
• ALP + GGT elevated together: Strongly suggests bile duct disease—cholangitis (inflammation) or obstruction. Cats need ultrasound promptly.
• All enzymes mildly elevated: Often secondary to another disease (hyperthyroidism, diabetes, pancreatitis) rather than primary liver disease.
• AST elevated but ALT normal: Usually muscle damage, not liver. Could be from a fall, seizures, or injection site reaction.

Understanding Each Liver Enzyme

ALT (Alanine Aminotransferase)

ALT is the most liver-specific enzyme in cats. It's found almost exclusively in liver cells, so elevated ALT almost always indicates liver damage. For a complete deep-dive on ALT including severity charts and hepatic lipidosis information, see our dedicated ALT guide.

• • Normal range: 10-120 U/L
• • Common causes of elevation: Hepatic lipidosis, hyperthyroidism, cholangiohepatitis, toxins
• • Key point: The most sensitive early indicator of liver cell damage

ALP (Alkaline Phosphatase)

ALP is found in bile ducts and bone. Unlike dogs, cats rarely have benign ALP elevations — any increase over 111 U/L is clinically significant and warrants investigation. For detailed severity charts and hepatic lipidosis patterns, see our dedicated ALP guide.

• • Normal range: 14-111 U/L
• • Common causes of elevation: Cholangitis, bile duct obstruction, hyperthyroidism, bone tumors
• • Key point: High ALP + high GGT strongly suggests bile duct disease

AST (Aspartate Aminotransferase)

AST is found in both liver cells AND muscle cells. This means elevated AST could indicate liver damage OR muscle injury — you need to check ALT and CK to distinguish. For a complete guide on interpreting AST including how to determine if it's liver vs muscle, see our dedicated AST guide.

• • Normal range: 9-39 U/L
• • High AST + High ALT: Liver damage confirmed
• • High AST + Normal ALT: Likely muscle damage (trauma, seizures, injections)
• • Key point: Always interpret AST alongside ALT

GGT (Gamma-Glutamyl Transferase)

GGT is highly specific to bile ducts. When elevated alongside ALP, it strongly suggests cholangitis (bile duct inflammation) or bile duct obstruction. See our GGT guide for detailed information.

• • Normal range: 1-10 U/L
• • Common causes of elevation: Cholangitis, bile duct obstruction, liver cancer
• • Key point: GGT + ALP elevated together = urgent ultrasound recommended

Symptoms Pet Owners Might Notice

• • Weight loss despite normal eating
• • Poor appetite or complete food refusal
• • Vomiting or diarrhea
• • Increased thirst and urination
• • Lethargy or hiding behavior
• • Jaundice (yellowing of eyes, gums, or inner ears)

What Happens Next?

Your veterinarian may recommend:

• • Repeat bloodwork to confirm trends
• • Liver ultrasound to assess structure and look for masses
• • Bile acids test to evaluate liver function
• • Testing for hyperthyroidism (common in older cats)
• • Testing for pancreatitis which often occurs alongside liver issues
• • Fine needle aspirate or biopsy for definitive diagnosis

Remember: Elevated liver enzymes are a signal, not a diagnosis. The pattern of elevation combined with your cat's history and clinical signs determines the next steps.

Related Reading

• • Cat ALT Levels Explained – deep dive on ALT, the most liver-specific enzyme
• • GGT Levels in Cats – understanding this bile duct-specific enzyme
• • Cat CBC Explained – understanding your cat's complete blood count alongside liver enzymes
• • Cat Kidney Values Explained – liver and kidney function often tested together
• • Transdermal Methimazole for Cats – treating hyperthyroidism, a common cause of elevated liver enzymes

Frequently Asked Questions