Quick answer
Vets use four cat kidney disease stages set by the International Renal Interest Society (IRIS). Stage 1 means kidney changes with normal creatinine, stage 2 mild, stage 3 moderate and stage 4 severe loss of function, based on blood creatinine and SDMA in a stable, hydrated cat. Stage is then refined by urine protein and blood pressure, and it guides treatment and outlook.
What is IRIS staging for cat kidney disease?
IRIS staging is the system vets worldwide use to grade chronic kidney disease (CKD) in cats and dogs. It was created by the International Renal Interest Society, a group of veterinary kidney specialists, and it’s updated as new research comes in.
Staging only happens after CKD has been diagnosed, and only in a stable, well-hydrated cat. A dehydrated cat or one with a blocked bladder can have high kidney values that drop once treated, so your vet may repeat the tests over a few weeks before assigning a stage.
There are two steps. First, blood creatinine and SDMA set the stage from 1 to 4. Then urine protein and blood pressure add a substage. If you’re new to the disease itself, start with our guide to cat kidney disease.
What are the 4 cat kidney disease stages?
These are the feline ranges from the IRIS Pocket Guide to CKD (June 2026). Creatinine is shown in the US unit (mg/dL) with the international unit in brackets.
| Stage | What it means | Creatinine | SDMA |
|---|---|---|---|
| Stage 1 | Kidney changes, no azotemia | Under 1.6 mg/dL (under 140 µmol/L) | Under 18 µg/dL |
| Stage 2 | Mild azotemia | 1.6 – 2.8 mg/dL (140 – 250 µmol/L) | 18 – 25 µg/dL |
| Stage 3 | Moderate azotemia | 2.9 – 5.0 mg/dL (251 – 440 µmol/L) | 26 – 38 µg/dL |
| Stage 4 | Severe azotemia | Over 5.0 mg/dL (over 440 µmol/L) | Over 38 µg/dL |
“Azotemia” means waste products are building up in the blood.
A cat in stage 1 has normal creatinine but another sign of kidney disease, such as dilute urine, protein in the urine, abnormal kidneys on ultrasound or an SDMA that stays above 14 µg/dL.
If creatinine and SDMA point to different stages, IRIS advises retesting both in 2 to 4 weeks. Cats with low muscle mass can have a falsely low creatinine, and if the results stay mismatched, vets usually assign the higher stage.
Substages: urine protein and blood pressure
| Measure | Normal | Borderline | High |
|---|---|---|---|
| Urine protein (UPC ratio) | Under 0.2 | 0.2 – 0.4 | Over 0.4 (proteinuric) |
| Systolic blood pressure | Under 140 mm Hg | 140 – 159 (prehypertensive) | 160 – 179 hypertensive, 180 or more severely hypertensive |
A cat’s full stage might read “stage 2, proteinuric, normotensive.” Protein in the urine and high blood pressure both speed up kidney damage, so they’re treated at every stage.
How is kidney disease treated at each stage?
Treatment builds as the stage rises. This follows the IRIS treatment recommendations. Your vet will choose the medications and set every dose for your cat.
| Stage | Main treatment goals |
|---|---|
| Stage 1 | Fresh water always available. Avoid drugs that can harm the kidneys. Find and treat any underlying cause. Treat blood pressure if it stays above 160 mm Hg or the eyes are affected. Treat persistent urine protein. Monitor trends |
| Stage 2 | Everything in stage 1, plus a prescription kidney diet. Treat low potassium, poor appetite and nausea |
| Stage 3 | Everything in stage 2. Tighter phosphorus control, often with a phosphate binder. Treat acid buildup in the blood, anemia and vomiting. Fluids under the skin may be needed |
| Stage 4 | Everything above. A feeding tube may be considered to help with nutrition, water and medicines |
IRIS also sets phosphorus targets that get looser by stage: under 4.6 mg/dL in stages 1 and 2, under 5.0 in stage 3 and under 6.0 in stage 4.
At every stage, your cat has less kidney function to spare, which makes human painkillers especially dangerous. Ibuprofen and aspirin can push a stable cat into sudden kidney failure, and acetaminophen harms a cat’s blood and liver. Ask your vet before giving any medicine.
What does stage 3 kidney disease mean for a cat?
Stage 3 means moderate loss of kidney function. Most cats now show signs: drinking and peeing more, losing weight, eating less and sometimes vomiting. It’s often the stage at which owners first notice something is wrong.
At this point, care focuses on keeping your cat eating and hydrated. That usually means a kidney diet, a phosphate binder, anti-nausea and appetite medicine, and often fluids under the skin that you can learn to give at home. Rechecks are usually more frequent, around every 2 to 3 months.
Many of these cats still have a good quality of life for a long time. Watch for weight loss, refusing food for more than a day and more frequent vomiting, and call your vet if they happen. Our should I take my cat to the vet? checker can help you decide how quickly.
What is the life expectancy for each kidney disease stage?
Life expectancy varies a lot between cats. It depends on how fast the disease progresses, whether protein loss and blood pressure are controlled, and whether your cat keeps eating.
| Stage at diagnosis | Typical outlook |
|---|---|
| Stage 1 | Often many years, since kidney function is still close to normal |
| Stage 2 | 2 to 3 years on average (Cornell Feline Health Center) |
| Stage 3 | Often 1 to 2 years in published studies, longer with good control |
| Stage 4 | Less than 6 months on average (Cornell Feline Health Center) |
These are averages, not predictions. Some cats live far beyond them. Kidney disease often goes along with other problems in older cats, such as hyperthyroidism, and treating those can change the picture.
How can I track my cat’s kidney stage at home?
You can’t stage kidney disease at home, but you can spot changes early and bring useful notes to each recheck.
- Weigh your cat every 2 to 4 weeks on the same scale. Steady weight loss is an early warning.
- Notice how much your cat drinks and how big the litter clumps are. More of either is worth mentioning.
- Keep copies of every blood and urine result so you can see trends over time.
- Write down appetite changes and any vomiting.
Regular rechecks are the key cost of kidney care. See what a cat vet visit costs to plan ahead, and browse more cat health problems.
Frequently asked questions
Can a cat go back to an earlier kidney stage?
Sometimes the numbers improve once a dehydrated cat is rehydrated or another problem is treated, which is why vets stage only a stable cat. True chronic kidney damage doesn't reverse, but good care can keep a cat in the same stage for a long time.
How often should a cat with kidney disease have bloodwork?
Most stable cats are rechecked every 3 to 6 months, and more often in stages 3 and 4 or after a change in treatment. Your vet will set the schedule.
What is a normal creatinine level for a cat?
IRIS uses a creatinine below 1.6 mg/dL (140 µmol/L) as the non-azotemic range for stage 1 in cats. Your lab's reference range may differ slightly, so ask your vet how your cat's result compares.
Sources
Written by the CatsMed Team from the sources above. This guide isn’t reviewed by a veterinarian and isn’t a substitute for one. See how we research.
