ALT is an enzyme found almost exclusively inside the cells of the liver. While it is primarily a "liver value," it is a staple of the chemistry panels used to monitor cats with Chronic Kidney Disease. In a renal patient, ALT serves as a vital indicator of the liver's health, which must remain strong to process medications and toxins that the kidneys can no longer handle.
The "Leakage" Enzyme
ALT is a "leakage" enzyme. Under normal conditions, it stays inside the liver cells (hepatocytes).
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The Release: When liver cells are damaged, inflamed, or dying, their membranes become permeable or burst, and ALT "leaks" into the bloodstream.
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The Magnitude: The higher the ALT level, the more widespread the liver cell damage usually is. However, ALT doesn't tell us about liver function (how well the liver is working), only that liver cells are currently being injured.
Why ALT is Relevant for CKD Cats
The liver and kidneys are the body's primary filtration duo. If the kidneys are failing, the liver often has to work harder.
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Medication Processing: Many medications used for CKD (like blood pressure meds or appetite stimulants) are processed by the liver. If ALT is high, the vet may need to adjust dosages to avoid overwhelming the liver.
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Hepatic Lipidosis (Fatty Liver): This is a major risk for CKD cats. If a renal cat stops eating due to nausea, their body begins to move fat to the liver to use for energy. Cats' livers are not good at processing this fat, leading to "Fatty Liver Disease," which causes a massive spike in ALT.
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Toxic Load: High levels of uremic toxins (BUN and Creatinine) can sometimes cause secondary "reactive" inflammation in the liver, leading to a mild rise in ALT.
High ALT (Hyperalaninemia)
In a CKD cat, a high ALT can be caused by:
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Hyperthyroidism: This is very common in senior cats alongside CKD. High thyroid levels are directly toxic to the liver and frequently cause a moderate rise in ALT.
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Dental Disease: Bacteria from infected teeth can enter the bloodstream and travel to the liver, causing inflammation.
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Low Oxygen (Hypoxia): As we discussed in the Anemia sections, if the blood is too thin, the liver doesn't get enough oxygen, which can cause liver cells to leak ALT.
[Image showing the anatomical relationship between the liver and the kidneys in a cat]
Interpreting the Results
ALT is measured in U/L (Units per Liter).
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Normal: Generally 20 to 100 U/L.
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Mild Elevation: 100 to 250 U/L. Often seen with "reactive" changes from other illnesses, dental disease, or early hyperthyroidism.
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Significant Elevation: Above 300 U/L. Suggests active liver disease, toxicity, or the onset of Hepatic Lipidosis.
Management
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Nutrition: The best way to protect a CKD cat's liver is to ensure they keep eating. If a cat is nauseous, using anti-nausea meds like Cerenia can prevent the "Fatty Liver" cycle.
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Denamarin/SAMe: If ALT remains high, vets often prescribe antioxidants like S-Adenosylmethionine (SAMe) to help protect liver cell membranes and promote repair.
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Thyroid Check: If ALT is high in an older CKD cat, a Total T4 test is almost always performed to rule out hyperthyroidism.
Disclaimer: This content is for educational purposes only and does not constitute veterinary medical advice. Always consult with your primary care veterinarian or a veterinary internal medicine specialist regarding your cat’s specific condition.