Liver & Metabolism Markers

While the kidneys filter waste, the liver is the body's chemical factory. It processes nutrients, detoxifies drugs, and creates the proteins essential for life.

For a cat with Chronic Kidney Disease (CKD), liver values are critical for two reasons:

  1. The "Triad" Effect: Older cats often develop multiple conditions at once. CKD, Hyperthyroidism, and Liver Disease frequently occur together.

  2. The Nutrition Check: These values tell us if your cat is eating enough protein to maintain their muscle mass and immune system, which is a major challenge in CKD management.

Here is your guide to decoding the liver and protein section of the blood panel.

1. The "Leakage" Enzymes: ALT and AST

These enzymes live inside the liver cells. In a healthy cat, they stay inside. If you see high levels in the blood, it means liver cells are being damaged and "leaking" their contents.

ALT (Alanine Aminotransferase)

  • Normal: 10–100 U/L

  • What it is: The most specific marker for liver cell damage (Hepatocellular Injury).

  • The Nuance: The magnitude matters. A mild elevation (2x normal) might be from hyperthyroidism or dental disease. A massive elevation (10x normal) suggests a toxin or acute trauma.

  • CKD Context: Many drugs used for CKD (like antibiotics or pain meds) are metabolized by the liver. If ALT rises, your vet may need to adjust dosages.

AST (Aspartate Aminotransferase)

  • Normal: 10–60 U/L

  • What it is: An enzyme found in the liver but also in muscles and red blood cells.

  • The Nuance: Because it is not unique to the liver, high AST alone doesn't prove liver disease.

  • The Tip: Look at Creatine Kinase (CK). If AST and CK are both high, the damage is likely in the muscles (perhaps from a struggle during blood draw or a fall). If AST and ALT are high, the damage is likely in the liver.

2. The "Flow" Enzymes: ALP and GGT

These enzymes measure Cholestasis—a fancy word for "blocked bile flow." Bile is the digestive fluid the liver makes. If the plumbing is backed up, these enzymes rise.

ALP (Alkaline Phosphatase)

  • Normal: 10–65 U/L

  • The "Cat Rule": In dogs, high ALP is common and often benign (stress, age). In cats, ALP is different. The "half-life" of ALP in a cat is only 6 hours (vs. 72 hours in dogs). This means the body clears it incredibly fast.

  • The Takeaway: Any elevation of ALP in a cat is significant. It almost always indicates active disease—either in the liver (lipidosis, cholangitis) or uncontrolled Hyperthyroidism.

GGT (Gamma-Glutamyl Transferase)

  • Normal: 0–1 U/L

  • What it is: A specific marker for the bile ducts.

  • The Nuance: It is less sensitive than ALP but more specific. If both ALP and GGT are high, the cat likely has Triaditis (inflammation of the liver, pancreas, and gut), a common comorbidity in CKD cats.

3. The Function Tests: Is the Factory Working?

Enzymes tell us if cells are damaged. These next markers tell us if the liver is actually doing its job.

Bilirubin

  • Normal: 0.1–0.4 mg/dL

  • What it is: A yellow pigment from recycled red blood cells. The liver is supposed to filter it out.

  • The Danger Signal: If the liver stops working or the bile duct is blocked, bilirubin builds up in the blood.

  • At Home Symptom: Jaundice (Icterus). You will see a yellow tint in the whites of the eyes, the gums, or the inside of the ears. This is a medical emergency.

Albumin

  • Normal: 2.5–3.9 g/dL

  • What it is: The most abundant protein in the blood. It acts like a sponge, holding water inside the blood vessels so it doesn't leak into tissues. It is made 100% by the liver.

  • The CKD Connection:

    • Low Albumin: Can mean the liver isn't making it (liver failure) OR the kidneys are leaking it out (Protein-Losing Nephropathy). If albumin gets too low (< 1.5), fluid leaks into the belly (ascites) or chest (pleural effusion).

    • High Albumin: Almost always means Dehydration. Since CKD cats are prone to dehydration, a "normal" albumin in a dehydrated cat might actually be low once they are rehydrated.

Globulins

  • Normal: 2.5–5.3 g/dL

  • What it is: These are your cat's antibodies (immune system proteins).

  • The Nuance:

    • High: Chronic inflammation or infection (like bad teeth, stomatitis, or Pyelonephritis).

    • Gap: Vets look at the "Albumin/Globulin Ratio." A low ratio often points to FIP (Feline Infectious Peritonitis) or severe inflammation.

Total Protein (TP)

  • Normal: 6.0–8.0 g/dL

  • What it is: Simply Albumin + Globulins.

  • The Hydration Check: In a CKD cat, we often use TP to check hydration status. If TP is high (e.g., 8.5), the blood is too concentrated, and the cat needs fluids.

Summary for the Caretaker

Liver markers add color to the black-and-white picture of CKD.

  • High ALT? Check for toxins or hyperthyroidism.

  • High ALP? Take it seriously—the liver is under stress or the thyroid is uncontrolled.

  • Low Albumin? Focus on nutrition and check the urine for protein loss (UPC ratio).

References

  • Center, S. A. (2009). Interpretation of Liver Enzymes. Veterinary Clinics: Small Animal Practice, 39(3), 439–472.

  • Bain, P. J. (2011). Liver. Duncan and Prasse's Veterinary Laboratory Medicine: Clinical Pathology.

  • Sparkes, A. H., et al. (2016). ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. Journal of Feline Medicine and Surgery.

  • Webb, C. B. (2018). Feline Inflammatory Liver Disease. Veterinary Clinics: Small Animal Practice.