AST (aspartate aminotransferase) is an enzyme found in liver cells, muscle cells, and heart tissue. When these cells are damaged, AST leaks into the bloodstream. Normal range: 9-39 U/L. Unlike ALT, AST is NOT liver-specific — it can rise from muscle injury too.

What is normal AST range for cats?

Normal AST range for cats is typically 9-39 U/L, though this varies by laboratory. AST has a very short half-life in cats (about 80 minutes), so elevations indicate recent or ongoing damage.

What causes high AST in cats?

High AST in cats can come from liver damage (hepatic lipidosis, cholangiohepatitis, FIP) OR muscle damage (trauma, seizures, injections, cardiac disease). Check ALT and CK levels to determine the source: if ALT is also high, it's liver; if CK is high but ALT normal, it's muscle.

When should I worry about AST in cats?

Worry when: AST is over 200 U/L with elevated ALT (suggests significant liver damage), your cat is showing symptoms (lethargy, not eating, jaundice), or AST is elevated with normal ALT in a cat with breathing difficulty or heart issues (may indicate cardiac disease).

Why does AST have a short half-life in cats?

AST has a half-life of about 80 minutes in cats (compared to 22 hours in dogs). This means AST levels drop quickly once the source of damage stops. Elevated AST in cats indicates recent or ongoing tissue damage.

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

Q: How do I know if high AST is from liver or muscle?

Check the ALT and CK (creatine kinase) levels. High AST + High ALT = liver damage. High AST + Normal ALT + High CK = muscle damage. High AST + Normal ALT + Normal CK = may need further investigation, could be cardiac.

Q: Is AST or ALT more important in cats?

Both are important but serve different purposes. ALT is more liver-specific, making it a better marker for liver disease. AST is more sensitive — it can detect some liver conditions (like FIP-related hepatitis) earlier than ALT, but it's less specific because muscle damage also raises AST.

Q: Can hyperthyroidism cause high AST in cats?

Yes. Hyperthyroidism can mildly elevate AST (along with ALT and ALP). The increased metabolic rate affects multiple tissues. AST typically normalizes once hyperthyroidism is treated.

Quick Answer: Normal AST in Cats

Normal AST range: 9-39 U/L. Unlike ALT, AST is found in liver AND muscle — so high AST could mean liver damage OR muscle injury. Check ALT and CK levels to determine the source.

If your cat's bloodwork shows elevated AST, this guide explains what it means, how to interpret it alongside other values, and what steps to take next. The key is understanding where the AST is coming from.

What is AST in Cats?

AST (Aspartate Aminotransferase) is an enzyme found in multiple tissues: skeletal muscle (highest concentration), liver, and heart muscle. When any of these tissues are damaged, AST leaks into the bloodstream.

This is the key difference from ALT: while ALT is highly liver-specific, AST is NOT. An elevated AST could indicate liver disease, muscle trauma, or even cardiac problems.

However, in cats, AST is actually more sensitive than ALT for detecting some liver conditions. AST is often elevated before ALT in conditions like feline infectious peritonitis (FIP) hepatitis. The short half-life of AST in cats (about 80 minutes) means elevations indicate recent or ongoing damage.

AST Severity Chart: Understanding Your Cat's Results

9-39 U/L

Normal

Meaning: Enzyme levels within healthy range

Action: Routine monitoring as part of wellness exams

40-117 U/L

Mild

Meaning: Minor tissue stress — could be muscle or liver (2-3x normal)

Action: Check ALT and CK to determine source, recheck in 2-4 weeks

118-195 U/L

Moderate

Meaning: Significant tissue damage — investigate source (3-5x normal)

Action: Check ALT, CK, consider ultrasound if liver suspected

196-390 U/L

Severe

Meaning: Serious tissue damage, often acute event (5-10x normal)

Action: Urgent workup, determine if liver or muscle origin

>390 U/L

Critical

Meaning: Severe acute damage — trauma, toxin, or massive liver injury (>10x normal)

Action: Emergency evaluation, stabilization, identify source immediately

AST Level (U/L)	Severity	What It Means	Typical Action
9-39	Normal	Enzyme levels within healthy range	Routine monitoring as part of wellness exams
40-117	Mild	Minor tissue stress — could be muscle or liver (2-3x normal)	Check ALT and CK to determine source, recheck in 2-4 weeks
118-195	Moderate	Significant tissue damage — investigate source (3-5x normal)	Check ALT, CK, consider ultrasound if liver suspected
196-390	Severe	Serious tissue damage, often acute event (5-10x normal)	Urgent workup, determine if liver or muscle origin
>390	Critical	Severe acute damage — trauma, toxin, or massive liver injury (>10x normal)	Emergency evaluation, stabilization, identify source immediately

The Critical Question: Liver or Muscle?

When AST is elevated, the most important step is determining the source. Here's how to tell:

High AST + High ALT: Liver damage is the source. Both enzymes are released from damaged liver cells.
High AST + Normal ALT + High CK: Muscle damage is the source. CK (creatine kinase) is muscle-specific.
High AST + Normal ALT + Normal CK: May indicate cardiac muscle damage or resolving muscle injury (CK has shorter half-life than AST).

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Common Causes of High AST in Cats

Liver-Related Causes

Hepatic Lipidosis (Fatty Liver): The most common liver disease in cats. AST and ALT both elevated.
Cholangiohepatitis: Inflammation of bile ducts and liver. Common in cats, often part of triaditis.
Feline Infectious Peritonitis (FIP): AST may be more sensitive than ALT for detecting FIP hepatitis.
Hyperthyroidism: Very common in older cats, causes mild AST and ALT elevation.
Toxin Exposure: Medications, lilies, chemicals can damage liver cells.
Liver Cancer: Lymphoma is most common in cats.

Muscle-Related Causes

Trauma or Falls: Impact injuries damage muscle cells, releasing AST.
Seizures: Prolonged muscle contractions cause muscle damage.
Injection Site Reactions: IM injections can cause local muscle damage.
Cardiac Disease: Heart muscle damage releases AST (heart is muscle tissue).
Prolonged Restraint: Struggling during exams or procedures can cause minor muscle damage.

Why AST Half-Life Matters

AST has a very short half-life in cats — approximately 80 minutes (compared to 22 hours in dogs). This means:

• AST levels drop quickly once the source of damage stops
• Elevated AST indicates recent or ongoing tissue damage
• If AST is elevated, the damage is happening NOW or happened very recently
• Serial measurements can track whether damage is resolving

AST vs ALT: When to Use Each

In cats, AST and ALT have complementary roles:

ALT is more specific: If ALT is elevated, it's almost certainly from the liver.
AST is more sensitive: AST may detect some liver conditions (like FIP hepatitis) before ALT rises.
Both together: When both AST and ALT are elevated, liver disease is confirmed. The ratio can help determine the type.

Symptoms Pet Owners Might Notice

Cats with elevated AST may show:

• Loss of appetite (if liver-related)
• Lethargy or hiding
• Limping or reluctance to move (if muscle-related)
• Vomiting or diarrhea
• Jaundice — yellow eyes, gums, or ear flaps (liver disease)
• Breathing difficulty (if cardiac-related)

Note: Many cats with elevated AST have no obvious symptoms, especially if the cause is muscle-related.

What Happens Next?

Your veterinarian may recommend:

• Check ALT level — confirms or rules out liver as source
• Check CK (creatine kinase) — confirms or rules out muscle as source
• Thyroid testing (T4) — hyperthyroidism is common in older cats
• Abdominal ultrasound — visualize liver if liver disease suspected
• Cardiac workup — if heart disease is suspected (echocardiogram)
• Recheck bloodwork — AST should drop quickly if source resolved

Key Takeaway

AST elevation requires context. Always interpret it alongside ALT and CK levels.

High AST alone doesn't tell you much — but high AST with high ALT confirms liver involvement, while high AST with high CK confirms muscle damage.

Understand Your Cat's AST Results

Upload your bloodwork to VetLens and instantly see:

✓ What your cat's specific AST level means
✓ Whether ALT suggests liver involvement
✓ How all values connect to form the full picture
✓ Questions to ask your vet at the next visit

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Frequently Asked Questions

Is AST or ALT more important in cats?

Both matter, but ALT is more liver-specific. AST is more sensitive for some conditions but less specific since it also rises with muscle damage. Use them together.

How do I know if high AST is from liver or muscle?

Check ALT and CK levels. High ALT = liver source. High CK with normal ALT = muscle source.

Why does AST drop faster than ALT in cats?

AST has a half-life of about 80 minutes in cats, while ALT persists longer. This makes AST useful for detecting recent damage but less useful for monitoring chronic conditions.

Can injections cause high AST in cats?

Yes. Intramuscular injections can cause local muscle damage that releases AST. This is usually mild and resolves quickly.

What is CK and why does it matter with AST?

CK (creatine kinase) is muscle-specific. When AST is elevated, checking CK helps determine if the source is muscle damage. High CK + High AST = muscle. Normal CK + High AST + High ALT = liver.

Can hyperthyroidism cause high AST in cats?

Yes. Hyperthyroidism can mildly elevate AST, ALT, and ALP. The increased metabolic rate stresses multiple organs. Values typically normalize with treatment.

Is high AST always serious?

Not necessarily. Mild elevations from injection site reactions or brief exertion often resolve without treatment. However, significant elevations or AST elevation with symptoms warrants investigation.

What is a normal AST level in cats?

Normal AST range is typically 9-39 U/L, though this varies by laboratory and testing method.