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Diagnostic Test🐕 Dogs🐈 Catsgastrointestinal

Alanine Aminotransferase (ALT)

🗣️ Pronounced:AL-uh-neen uh-MEE-noh-TRANS-fer-ays
In One Sentence (Plain English)

A liver enzyme found inside liver cells that leaks into the bloodstream when hepatocytes are damaged or inflamed.

Editorial Status: Verified from peer-reviewed veterinary sources (v1.0)
Updated: 2026-01-15

💬 In Plain English

ALT is the premier "leakage enzyme" for liver health in dogs and cats. The cells of the liver (hepatocytes) are filled with ALT. When liver cells are injured, inflamed, starved of oxygen, or exposed to toxins, their microscopic outer membranes become leaky, spilling ALT directly into the bloodstream. A high ALT number tells your veterinarian that liver cells are actively being injured or dying right now. However, ALT is a marker of cellular damage, not liver function—meaning a dog can have high ALT while the liver is still successfully processing toxins.

🔬 Clinical & Technical Depth

For Vets & Technicians

Formal Clinical Definition

Cytoplasmic leakage enzyme specific to hepatocytes in canines and felines. Elevated serum activity reflects hepatocellular membrane damage, necrosis, or regeneration, with an elimination half-life of roughly 40 to 60 hours in dogs and much shorter (several hours) in cats.

Why Veterinarians Use It

Veterinarians assess ALT on routine blood panels to detect acute hepatitis, toxic liver insults (like sago palm or xylitol), trauma, or drug-induced liver stress.

Clinical Context Encountered

Found on almost every standard chemistry profile; investigated when elevated above reference intervals (typically >100–120 U/L).

Clinical Reference Guide (Diagnostic Test)

Sample Required
Patient Preparation
🚨 Red Flag Warnings (When to Contact an Emergency Vet)
  • •A sudden massive spike in ALT (>1,000–5,000 U/L) indicates acute hepatocellular necrosis from toxic ingestion (xylitol, blue-green algae, acetaminophen) or severe circulatory shock requiring immediate hospitalization.

❓ Questions to Ask Your Veterinarian

Take these actionable questions with you to your next clinic visit or appointment:

  • 1How high is the ALT elevation (mild 2x, moderate 3–5x, or marked >10x above normal)?
  • 2Are other liver enzymes like ALP, GGT, and total bilirubin elevated as well?
  • 3Are true liver function markers (albumin, BUN, cholesterol, glucose, bile acids) normal?
  • 4Would starting a liver antioxidant supplement like SAMe/silybin (Denamarin) be beneficial?

Academic & Clinical References

  • ASVCP Guidelines on Liver Enzyme Interpretation in Small Animals
    Organization: American Society for Veterinary Clinical Pathology (ASVCP) • Accessed: 2026-01-10
    https://www.asvcp.org