Cat Kidney Disease Stages Explained: IRIS Staging, Diet and Monitoring

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Chronic kidney disease is the most common illness of older cats, and many owners hear the word stage at the vet without knowing what it means. Staging is a tool that helps your vet match treatment to your cat. This guide explains it in plain terms, and complements chronic kidney disease in cats.

Why vets stage kidney disease

Kidney disease is not a single condition with a single treatment. A cat with mild changes needs different care from one in advanced failure. IRIS, an international group of kidney specialists, created a staging system that is widely used. It helps vets decide on diet, medication, monitoring and prognosis.

How staging works

Staging is done when the cat is well hydrated and stable, ideally with repeat tests. It is based on two key blood markers:

• Creatinine. A waste product that rises as kidney function falls.
• SDMA. A marker that rises earlier than creatinine, and helps to identify early disease.

Then vets add sub-stages:

• Proteinuria. Protein in the urine, measured as a urine protein to creatinine ratio, shows kidney damage, and affects treatment.
• Blood pressure. High pressure damages the kidneys and other organs. See high blood pressure in cats.

See cat blood tests explained.

The four stages

Stage 1. Kidney values are normal or only slightly changed, but there is evidence of disease, such as abnormal urine concentration, protein in the urine or imaging changes. Cats usually have no signs.

Stage 2. Mild increase in creatinine or SDMA. Signs may be mild or absent, such as slightly more thirst and urination.

Stage 3. Moderate increase. Signs are usually present: weight loss, reduced appetite, nausea, increased thirst, poor coat and sometimes anemia.

Stage 4. Severe increase. Cats are often very unwell, with vomiting, poor appetite, dehydration, weakness, mouth ulcers and electrolyte problems.

Treatment by stage

Stages 1 and 2

• Find and treat underlying causes, such as infection, stones or high blood pressure.
• Encourage drinking, and feed wet food. See how to get a cat to drink more water.
• Start a kidney diet, in stage 2 for most cats, as advised.
• Monitor blood pressure and protein.
• Recheck every three to six months.

Stage 3

• Kidney diet, with reduced phosphorus and good quality protein.
• Subcutaneous fluids, in some cats. See how to give a cat subcutaneous fluids.
• Phosphate binders, if phosphorus is high.
• Anti-nausea medication and appetite stimulants.
• Treatment for anemia, potassium problems and high blood pressure.
• Recheck every two to three months.

Stage 4

• Intensive support: fluids, anti-nausea drugs, appetite stimulants, phosphate binders, nutrition support such as a feeding tube.
• Pain and comfort care.
• Frequent rechecks.
• Discussions about quality of life. See cat quality of life and saying goodbye.

Diet

Prescription kidney diets restrict phosphorus, which slows progression, and provide controlled protein, omega-3 fatty acids and added potassium. Cats often refuse them, so transition slowly, and try different brands and flavors, in wet and dry forms. A cat that eats well on a normal food may be better off than one that refuses a kidney diet. See how to switch cat foods. Ask your vet before using home-cooked or supplement-based approaches.

Home monitoring

• Weigh monthly.
• Note thirst, urine volume, appetite and vomiting.
• Look at the coat and mouth.
• Keep a log for rechecks.
• Give medicines on time.

Outlook

Survival varies by stage at diagnosis: cats in stage 2 often live several years, stage 3 more than a year in many cases, and stage 4 months. Many cats have good quality of life through the stages with proper care.

Insurance and cost

Ongoing care adds up. See cat pet insurance guide and low-cost vet care for cats.

Proteinuria and blood pressure sub-staging

Protein in urine is both a sign and a cause of kidney damage. Vets classify cats as non-proteinuric, borderline or proteinuric. Cats with significant protein loss may be given medication such as telmisartan to reduce it. Blood pressure is also classified as normal, borderline, hypertensive or severely hypertensive, and treated with amlodipine if needed. These details shape the plan as much as the creatinine value does. See high blood pressure in cats.

Dehydration and acute flare-ups

Cats with kidney disease can have sudden worsening, for example after vomiting, a urinary infection or dehydration. This is called an acute-on-chronic episode. Prompt fluids and treatment can bring a cat back. If your cat stops eating or drinking, vomits or becomes lethargic, call the vet at once.

Anemia and potassium

Kidneys make a hormone that stimulates red blood cell production, so anemia develops in advanced disease. Low potassium can cause weakness, particularly in the neck, which may make a cat hold its head down. Both are treatable. Regular blood tests find them early.

Making quality of life central

At every stage, ask whether your cat is eating, grooming, playing, enjoying favorite spots and using the litter box. Keep a journal of good and bad days. When bad days begin to outnumber good ones, talk to your vet about comfort care. See cat quality of life and saying goodbye.

When to see a vet

See a vet if your cat has increased thirst, weight loss or poor appetite. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.