# High ALT in Cats: Causes and What to Do Next A high ALT on cat bloodwork means the liver enzyme alanine aminotransferase is above the normal range, which usually points to liver cell stress or damage. It does not tell your veterinarian why the liver is irritated, and many cats with a mild increase are fine with monitoring. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - ALT is a liver enzyme, and a high value means liver cells are leaking it into the blood, not that your cat's liver has failed. - Common causes include fatty liver, inflammation, infection, toxins, and other illnesses that affect the liver secondhand. - A mild rise with a normal exam and normal bile acids often just needs a recheck in a few weeks. - A marked rise, especially with vomiting, jaundice, or not eating, needs same-day veterinary care. - Never give your cat human medications, supplements, or leftover prescriptions while you wait for the recheck. ## What High ALT Looks Like and What Is Normal ### What the ALT blood test measures ALT lives inside liver cells. When those cells are injured or inflamed, ALT leaks into the bloodstream, so the number goes up. Your vet reads ALT alongside other values, including AST, bilirubin, and bile acids, to build a picture of liver function. ### Signs you might notice at home Many cats with a high ALT look completely normal. When signs do appear, they can include poor appetite, vomiting, weight loss, lethargy, or yellowing of the gums and skin. A cat with severe liver injury may also run a fever and seem withdrawn, as seen in one reported case where a cat had fever, lethargy, and inappetence alongside markedly increased ALT and AST [1]. ### What counts as normal Normal ALT ranges differ between laboratories, so compare your cat's result to the range printed on your own report. Mild increases are common and often temporary. Marked increases, or values that keep climbing on repeat testing, carry more concern. ## Main Causes of Elevated ALT in Cats | Cause | Typical clues | How urgent | |---|---|---| | Fatty liver (hepatic lipidosis) | Overweight cat that stopped eating, weight loss, jaundice | Emergency | | Liver inflammation or infection | Vomiting, fever, poor appetite, rising ALT and AST | Same-day to urgent | | Toxins (human drugs, plants, chemicals) | Known exposure, sudden vomiting, drooling, lethargy | Emergency | | Hyperthyroidism | Older cat, weight loss with good appetite, high TT4 | Routine visit | | Obesity-related liver stress | Overweight or obese body condition, high triglycerides | Routine visit | | Other illness affecting the liver | Signs tied to the primary disease, such as kidney or urinary problems | Depends on the primary cause | ### Fatty liver and sudden appetite loss Fatty liver is one of the most serious causes of a high ALT in cats. It usually follows a period of not eating, sometimes only a few days. Any cat that stops eating needs to be seen quickly, because fatty liver can worsen fast. ### Inflammation and infection Liver inflammation can come from infections, immune problems, or unknown triggers. In one case, a cat with severe liver injury had a mild neutrophilia with a regenerative left shift and moderate thrombocytopenia on blood work, and the cat recovered with hospitalization and supportive care [1]. That case also showed that a high ALT can return to normal with treatment. ### Toxins and medications Many human pain relievers, some plants, and certain chemicals are toxic to cats. If you know or suspect your cat swallowed something, call your vet or a pet poison hotline right away. Do not wait for symptoms. ### Hormones and other conditions Hyperthyroidism is the most common endocrine disorder in older cats, and ALT tracks closely with thyroid status during treatment. In one study, ALT correlated with TT4 levels from 0.919 to 0.981 across visits, and ALT changed significantly once treatment started [2]. That means a high ALT in a hyperthyroid cat may improve as the thyroid condition is controlled. ### Obesity and body condition Extra body fat affects liver values. In a study of sterilized cats, obese cats had higher ALT activity than cats at an ideal body condition score [3]. Another study found that cats with obesity disease had higher ALT activity along with higher triglycerides and serum amyloid A [4]. If your cat has been gaining weight, see [Cat Weight Gain Causes](/knowledge/veterinary-medicine/nutrition/cat-weight-gain-causes) for practical steps. ### Normal variation between tests Even healthy cats can have small swings in liver values from one week to the next. In a study of healthy cats and cats with chronic kidney disease, biochemistry analytes showed intermediate or high individuality, meaning each cat has its own baseline [5]. Your vet uses your cat's history and trend, not one number alone. ## Red Flags That Make It an Emergency Go to an emergency clinic now if your cat has any of these: - Yellow gums, skin, or whites of the eyes - Repeated vomiting or vomiting blood - Not eating for more than 24 hours - Collapse, seizures, or extreme weakness - Known or suspected exposure to a toxin - Rapid breathing or a swollen, painful belly These signs with a high ALT suggest serious liver injury or another urgent problem. Do not wait for a scheduled appointment. ## Safe Things You Can Do at Home While Waiting ### Keep your cat eating Appetite is the single most important thing you can watch. If your cat stops eating, call your vet the same day. Do not force food or water. ### Remove possible toxins Put away human medications, essential oils, and household chemicals. Check your houseplants against a pet poison list. If you suspect exposure, call for help immediately. ### Do not give any medication on your own Do not give human pain relievers, steroids, antibiotics, or supplements. Some are directly toxic to the liver. Your veterinarian calculates any dose from your cat's weight and health. ### Keep a simple log Write down what your cat eats each day, any vomiting, stool changes, and energy level. Bring the log to your appointment. This helps your vet decide whether the ALT is stable or worsening. ### Watch for other signs If you notice your cat overgrooming or losing hair, that can point to a separate problem. See [Cat Overgrooming: Why It Happens and What to Do](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-overgrooming) and [Cat Hair Loss on Ears: Causes and What to Do](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-hair-loss-on-ears). If you see blood in the urine, read [Cat Blood in Urine: Causes and When to Rush to the Vet](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-blood-in-urine-causes-when-to-rush) or, if your cat seems otherwise fine, [Cat Blood in Urine but Acting Normal: Causes and Next Steps](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-blood-urine-acting-normal). ## What Your Veterinarian Will Check and Test ### Physical exam and history Your vet will check your cat's weight, body condition, gum color, hydration, and belly. They will ask about appetite, diet changes, possible toxin exposure, and any medications. ### Repeat bloodwork A single high ALT is often repeated in a few weeks. If the value is falling, monitoring may be enough. If it is rising, more testing is needed. Trends matter more than one snapshot. ### Liver function and bile acids Bile acids help show how well the liver is working, separate from how irritated it is. Your vet may also check bilirubin, albumin, and glucose. ### Imaging X-rays or ultrasound can show liver size, shape, and texture. Ultrasound can also spot gallstones, masses, or fluid. These findings guide whether a biopsy is needed. ### Thyroid and other screening tests Because ALT tracks with thyroid status in hyperthyroid cats [2], your vet may check TT4, especially in cats over 8 years old. They may also screen for kidney disease, diabetes, and infections. ### When a biopsy is considered If the cause is still unclear after blood work and imaging, your vet may recommend a liver biopsy or fine needle aspirate. This is the most direct way to tell inflammation from cancer or other disease. ## Prevention and Monitoring ### Keep your cat at a healthy weight Obesity is linked to higher ALT and other metabolic changes in cats [3][4]. Ask your vet for a target weight and a measured feeding plan. Even small weight loss helps. ### Feed a consistent, balanced diet Sudden diet changes and long periods without food raise the risk of fatty liver. If you need to switch foods, do it slowly and keep your cat eating. ### Schedule regular wellness bloodwork Annual or twice-yearly blood work catches rising liver values before your cat shows signs. This matters most for cats over 8 and for cats on long-term medication. ### Manage chronic conditions If your cat has hyperthyroidism, kidney disease, or diabetes, keeping the primary condition controlled helps keep ALT stable. In hyperthyroid cats, ALT moves with thyroid status during treatment [2]. ### Recheck on schedule Your vet will set the recheck interval based on how high the ALT is and how your cat looks. Do not skip these visits, even if your cat seems fine. ## Limitations and When to Contact a Veterinarian A high ALT is a clue, not a diagnosis. The same number can mean something minor in one cat and something serious in another. Only your veterinarian can interpret your cat's full picture, and individual cases always need a veterinarian. Contact your vet the same day if your cat stops eating, vomits repeatedly, or seems painful or weak. Go to an emergency clinic now for jaundice, collapse, seizures, breathing trouble, or known toxin exposure. Schedule a routine visit for a mild ALT rise found on wellness blood work, especially if your cat is acting normal. Bring your feeding log and any medication list to that visit. ## Frequently Asked Questions ### Does a high ALT mean my cat has liver failure? No, a high ALT means liver cells are irritated or injured, not that the liver has stopped working. Many cats with a high ALT have normal liver function and recover. Your vet uses bile acids, bilirubin, and other tests to judge how well the liver is working. ### Can a high ALT go back to normal on its own? Yes, mild increases often return to normal once the trigger resolves. In one reported case, a cat with severe liver injury improved with hospitalization and supportive care, and ALT and AST were normal at follow-up [1]. That said, your vet still needs to find the cause. ### Should I change my cat's food because of a high ALT? Not without veterinary guidance. Diet changes are sometimes part of treatment, but the right choice depends on the cause. A sudden switch can also cause appetite loss, which is risky for the liver. ### How often should a cat with high ALT be rechecked? Your vet sets the schedule based on the value and your cat's signs. Many cats are rechecked in a few weeks, then again if the value is stable. Cats on treatment for another condition may be checked more often. ### Can hyperthyroidism cause a high ALT in cats? Yes, ALT tracks closely with thyroid status in hyperthyroid cats, with correlations from 0.919 to 0.981 across treatment visits [2]. Treating the thyroid condition often brings ALT down. Your vet may check thyroid levels if your cat is older and losing weight. ## Related Articles - [Cat Overgrooming: Why It Happens and What to Do](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-overgrooming) - [Cat Blood in Urine: Causes and When to Rush to the Vet](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-blood-in-urine-causes-when-to-rush) - [Cat Blood in Urine but Acting Normal: Causes and Next Steps](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-blood-urine-acting-normal) - [Cat Weight Gain Causes](/knowledge/veterinary-medicine/nutrition/cat-weight-gain-causes) - [Cat Hair Loss on Ears: Causes and What to Do](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-hair-loss-on-ears) - [Why Is My Cat suddenly going blind? Hypertensive Retinal Detachment and Uveitis](/knowledge/veterinary-medicine/symptom-guides/why-is-my-cat-suddenly-going-blind-hypertensive-retinal-detachment-and-uveitis) - [High Liver Enzymes in Cats: Causes and What Happens Next](/knowledge/veterinary-medicine/digestive-and-urinary-care/high-liver-enzymes-cats) - [High ALP in Cats: What the Blood Test Means](/knowledge/veterinary-medicine/vet-visit-decisions/cat-bloodwork-alp-high) - [High GGT in Cats: Liver Test Explained](/knowledge/veterinary-medicine/vet-visit-decisions/cat-bloodwork-ggt-high) ## References 1. [Blue-Green Neutrophilic Inclusions in a Cat With Severe Hepatocellular Injury](https://pubmed.ncbi.nlm.nih.gov/42667639/). Veterinary medicine and science, 2026. 2. [Haematological Tracking of Thyroid Status During Methimazole Therapy and After Treatment Interruption in Hyperthyroid Cats: A Prospective Longitudinal Cohort Study](https://pubmed.ncbi.nlm.nih.gov/42514716/). Veterinary sciences, 2026. 3. [Association of obesity-related blood chemistry alterations with animal welfare outcomes in sterilized cats: A case-control study in Indonesia](https://pubmed.ncbi.nlm.nih.gov/42494703/). Veterinary world, 2026. 4. [Establishing diagnostic criteria for feline obesity using a highly sensitive serum amyloid A assay](https://pubmed.ncbi.nlm.nih.gov/40678493/). Frontiers in veterinary science, 2025. 5. [Weekly biological variation of serum biochemistry analytes and fibroblast growth factor 23 in healthy cats and cats with chronic kidney disease](https://pubmed.ncbi.nlm.nih.gov/40579832/). The Journal of small animal practice, 2025. ## Further Reading - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)