Chronic kidney disease is a lasting loss of kidney function that gets worse over time. Cornell University's Feline Health Center says it affects up to 40% of cats over the age of 10 and 80% of cats over 15. Lost kidney tissue does not come back, but a kidney diet, enough water and treatment of the problems the disease causes can slow it down.
The kidneys filter the blood, make urine and help control blood pressure, Cornell explains. In chronic kidney disease they lose that ability bit by bit. The Merck Veterinary Manual says the disease often develops over months or years before it shows, and that by then it cannot be reversed.
Cornell says the only known risk factor is age. The Merck manual adds that a sudden kidney injury can turn into the chronic disease, and its owner pages say any part of a lily can cause such an injury in a cat. Lilies are on Toxic to cats.
In the early stages it is very common for a cat to show no obvious signs, Cornell says. Then the cat passes more urine and drinks more to keep up. Later it eats less, loses weight, looks unkempt and seems tired. The Merck manual's owner pages add sores in the mouth, vomiting and diarrhea as the disease moves on.
Cornell says about 60% of cats with kidney disease also develop high blood pressure, which can cause sudden changes in vision, disorientation and weakness. The kidneys also make the hormone that drives the making of red blood cells, so some cats become anemic, with pale gums, tiredness and a poor appetite.
Cornell says no single test gives the vet the full picture, and that kidney function is ideally judged on at least two blood and urine samples taken within two weeks of each other. The figures in this table are Cornell's.
| Test | What it measures | What the result tells the vet |
|---|---|---|
| Creatinine and urea (BUN), in blood | Two waste products that healthy kidneys filter out. | Both rise as the kidneys fail, but creatinine does not generally rise until almost 75% of kidney function is lost. Dehydration raises both. |
| SDMA, in blood | A third waste product. | Dehydration and muscle mass affect it less, and a rise can be detected when about 40% of kidney function is lost. |
| Urine concentration (specific gravity) | How well the kidneys save water. | Weak urine can be one of the earliest signs. The reading is falsely low in a cat that has just been given fluids. |
| Urine protein and urine culture | Protein leaking through the kidneys, and bacteria in the urine. | In some studies, cats that lose more protein have a less favorable outlook. The culture rules out an infection. |
| Blood pressure | The pressure in the arteries. | The FDA says untreated high blood pressure can damage a cat's eyes, kidneys, heart and brain. |
| Phosphorus, potassium and red blood cells | Minerals in the blood, and the blood count. | They show complications that can be treated. In some studies, higher phosphorus and fewer red cells go with a less favorable outlook. |
| Ultrasound and x-rays | Pictures of the inside of the belly. | Cornell lists them as useful when kidney disease is suspected. |
More on the samples and the pictures: blood tests, urine samples, x-rays and ultrasound.
Once the disease is confirmed, the vet gives it a stage. The International Renal Interest Society bases the stage on fasting blood creatinine, measured on at least two occasions in a stable cat, and adds sub-stages for urine protein and blood pressure. The Merck manual prints the society's creatinine bands for cats, in milligrams per deciliter.
| Stage | Creatinine | What the Merck manual says |
|---|---|---|
| Stage 1 | Below 1.6. | The kidneys are damaged, but the blood values have not risen and there are no signs. |
| Stage 2 | From 1.6 to 2.8. | The values are mildly raised. Signs are often not evident yet. |
| Stage 3 | From 2.9 to 5. | The values are moderately raised, and signs are often evident. |
| Stage 4 | Above 5. | The values are severely raised, and the risk of a crisis is higher. |
Cornell warns that a dehydrated or sick cat can look further along than it is.
A kidney diet comes first. These foods hold back protein, phosphorus and sodium, and Cornell says some studies show cats on a prescription kidney diet living two to three times longer than cats on ordinary cat food. In one study cited by the International Society of Feline Medicine, the median was 633 days on a kidney diet against 264 days on ordinary food. The Merck manual recommends the diet from stage 2.
Cornell says to change over gradually, because many cats are slow to accept the food. Do not let hunger decide: a cat with kidney disease that goes without food for even a short time can develop significant health problems.
Water is essential too. Cornell says dehydration can speed up the damage, and suggests wet food and bowls of fresh water in several places. Some cats, mostly in the later stages, need fluids under the skin every one to three days, which many owners learn to give at home.
Medicines treat the complications. The FDA has approved three liquids for cats:
Ask before you pay for two things. The Merck manual does not recommend acid-reducing medicine as a routine precaution, because stomach ulcers from kidney disease are uncommon in cats. Cornell describes dialysis and kidney transplants as complex, expensive and disputed, and says no studies have yet proved how well they work.
Cornell says the outlook varies a great deal with the stage and with how the cat responds to treatment. In many studies cats found at stage 2 lived two to three years on average, and cats found at stage 4 less than six months. Those are averages. Finding it early gives the best chance, which is why Cornell asks for regular exams and blood work for every senior cat. The schedule is on The senior checkup.
None of the sources read for this page prices a lifetime of kidney care. CareCredit publishes national averages for cats from a 2025 to 2026 cost study by Synchrony: $302 for a kidney disease exam, $144 for a chemistry panel, $54 for a urine test, $35 for a blood pressure reading and $323 for an ultrasound. More figures are on What does a vet bill cost? Help is on When you cannot pay the vet bill.
Call the vet the same day, or an emergency clinic at night, if a cat with kidney disease shows any of these:
All the signs are on Cats: is this an emergency?
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Sources read on 2 October 2026; every number is as the source gives it. The International Renal Interest Society's staging document could not be opened on that day, so the creatinine bands are given as the Merck Veterinary Manual prints them.