Kidney Disease In Cats Stages

Kidney disease in cats can feel overwhelming at first, especially when you start hearing terms like IRIS stages, creatinine, and subcutaneous fluids. The good news is that many cats with chronic kidney disease (CKD) live comfortably for years with the right plan and regular monitoring. In this article, I will walk you through the stages in clear language, what they mean, what signs to watch for, and how vets typically support cats at each step.

Quick note: This article is educational and not a substitute for veterinary care. If you are worried about your cat’s symptoms, call your veterinarian.

What kidney disease means

Your cat’s kidneys do more than make urine. They help regulate hydration, electrolytes, and blood pressure, and they support red blood cell production. Chronic kidney disease means the kidneys are gradually losing function over time. It is especially common in older cats.

CKD is different from acute kidney injury (AKI), which happens suddenly, often due to toxins (like lilies), urinary blockages, severe dehydration, or certain infections. AKI can sometimes improve significantly with emergency care, while CKD is usually managed long term.

It is also common for CKD cats to have other issues that affect how they feel and how fast the disease progresses. In the clinic, we often check for (and treat) things like dental disease and inflammation, hyperthyroidism, dehydration episodes, urinary tract infections, and high blood pressure.

How vets stage CKD (IRIS)

Most veterinary teams use the IRIS staging system (International Renal Interest Society). The stage itself is primarily based on a cat’s fasting creatinine (or SDMA) when they are stable and well hydrated. Then cats are substaged by blood pressure and protein in the urine.

What are creatinine and SDMA? They are markers that help estimate kidney filtration. Creatinine can be influenced by muscle mass, while SDMA may rise earlier in some cats. Your vet will usually look at the trend over time, not just a single number.

Urine testing (like urine specific gravity) is still very important. It supports diagnosis, helps interpret lab results, and can point to complications, but it is not the main value used to assign an IRIS stage.

Important note: A stage is not a “time left” prediction. Two cats in the same stage can do very differently depending on appetite, blood pressure, phosphorus control, protein in the urine, dental health, hydration, and how early the disease was detected.

What the stages mean

• Stage 1: Kidney changes may be present, but creatinine can be normal or near normal. Many cats have no obvious signs.
• Stage 2: Mild loss of kidney function. Many cats still act fairly normal, but early support makes a big difference.
• Stage 3: Moderate loss of function. Weight loss, nausea, and dehydration are more common.
• Stage 4: Severe loss of function. Cats often need intensive, customized support to maintain comfort and quality of life.

Stage 1: what to expect

What you might notice: Often nothing obvious. Some cats may drink a bit more water or urinate larger clumps in the litter box, but many Stage 1 cats are truly asymptomatic.

What the vet looks for: Early markers can include a rising SDMA, a mild upward trend in creatinine, changes in urine concentration, or imaging changes. Your vet will also check for other causes of increased drinking and urination, like hyperthyroidism or diabetes.

Common focus at this stage:

• Confirming the trend with repeat labs instead of relying on a single test
• Encouraging hydration, especially with wet food
• Checking blood pressure and urine for protein
• Considering screening for silent issues like a urinary infection when signs or urine results suggest it
• Setting a monitoring schedule so changes are caught early

Stage 2: common care

What you might notice: Increased thirst and urination become more consistent. Some cats start losing weight slowly, or they become pickier with food.

Common vet recommendations:

• Diet support: Many cats do best on a kidney-support diet. These diets typically restrict phosphorus and adjust nutrients carefully, including moderate, high-quality protein rather than simply “very low protein.” The right choice is individualized. If your cat refuses a prescription kidney diet, your vet can help you find realistic options because eating enough matters.
• Phosphorus management: Keeping phosphorus in a healthy range is strongly tied to stability in CKD. Sometimes this is diet alone, and sometimes phosphate binders are needed.
• Control nausea early: Mild nausea can show up as lip smacking, walking away from food, or “sniffing and leaving.” Treating nausea can protect appetite and weight.
• Monitor blood pressure: High blood pressure can silently damage the eyes, brain, and kidneys.
• Check urine and consider culture: Some CKD cats get urinary tract infections without obvious symptoms. When urinalysis suggests it, a urine culture can be a helpful next step.

Stage 3: what support looks like

What you might notice: More noticeable weight loss, dehydration, poor coat quality, bad breath (sometimes “uremic” breath), nausea, vomiting, and constipation. Some cats become less social or hide more because they feel crummy.

Common support at this stage:

• Hydration support: Many cats benefit from subcutaneous fluids at home. This is something your veterinary team can teach you step by step.
• Nausea and appetite support: This may include anti-nausea medications, stomach acid reducers, and appetite stimulants when appropriate.
• Phosphorus and gut support: Ongoing phosphorus control, constipation management, and in some cases support for stomach irritation or uremic ulcers.
• Electrolyte monitoring: Potassium can drop in CKD, contributing to weakness and poor appetite. Some cats need supplementation.
• Anemia monitoring: As kidney function declines, anemia can develop and worsen fatigue.
• Protein in urine (proteinuria): If present, your vet may recommend medications to reduce protein loss and protect kidney tissue.

Practical at-home tip: Keep a simple weekly log: weight, appetite, water intake changes, vomiting, stool quality, and energy. Small changes help your vet fine-tune the plan.

Stage 4: comfort-focused care

What you might notice: Significant appetite loss, frequent nausea, dehydration, muscle wasting, weakness, and “good days and bad days.” Some cats become very sensitive to stress and changes in routine.

Goals at this stage: Comfort, hydration, nutrition support, and minimizing nausea. Some cats still do well for a meaningful period with a carefully tailored plan, while others decline faster. Your vet can help you judge what is medically appropriate and what is fair to your cat’s quality of life.

Common care tools:

• More frequent lab and blood pressure checks to guide decisions
• Customized fluid schedules and nausea control
• Phosphorus control, constipation management, and stomach support when needed
• Quality-of-life check-ins, including mobility and the ability to eat and engage

Substaging: BP and protein

IRIS staging often includes two important “sub-stages” because they can speed up kidney damage if not addressed:

• Blood pressure: High blood pressure can be serious and sometimes has no outward signs until there is eye damage or sudden blindness.
• Proteinuria: Protein leaking into the urine can indicate ongoing kidney injury. Treating it can slow progression in many cases.

How often to recheck

It depends on stage, stability, and what treatments are being adjusted, but these are common patterns I see in practice:

• Stage 1: Often every 6 to 12 months (sooner if values are changing or there are symptoms)
• Stage 2: Often every 3 to 6 months
• Stage 3: Often every 2 to 3 months
• Stage 4: Often monthly or as needed to keep your cat comfortable

If your cat starts a new medication, diet change, fluid plan, or blood pressure therapy, your vet may recommend earlier follow-ups.

Early warning signs

In the clinic, I see so many loving families blame early kidney disease signs on “just getting older.” Keep an eye out for:

• Bigger urine clumps or more frequent scooping
• Drinking more, hanging out at faucets, or seeking unusual water sources
• Weight loss even when appetite looks okay
• Decreased grooming, dandruff, or a dull coat
• Bad breath, drooling, or mouth discomfort (dental disease can be a big contributor)
• Constipation or smaller, harder stools
• Hiding, less interest in play, or sleeping more than usual

Frequently asked questions

How is kidney disease diagnosed?

Diagnosis usually involves a combination of bloodwork (creatinine, BUN, SDMA, phosphorus), urinalysis (urine specific gravity, protein), and often blood pressure. Your vet may recommend imaging (x-ray or ultrasound) to evaluate kidney size and structure. Depending on symptoms and urine results, a urine culture may be recommended to look for an occult infection.

Can kidney disease be cured?

Chronic kidney disease is typically not curable, but it is very often manageable. The earlier we catch it and the more consistent the support, the better most cats feel.

What is the best food for a cat with CKD?

In general, foods formulated for kidney support help many cats, especially due to phosphorus restriction and careful nutrient balance. Renal diets usually use moderate, high-quality protein, not “no protein.” That said, the “best” food is the one your cat will reliably eat while meeting kidney needs as closely as possible. If appetite is a struggle, talk to your vet before making major changes.

How often should my cat be checked?

It depends on stage and stability. Many cats benefit from rechecks every few months, and more often when medications are being adjusted. Your vet will tailor this to your cat’s labs and symptoms.

When is it an emergency?

Seek urgent veterinary care if your cat stops eating for 12 to 24 hours (sooner for seniors or known CKD cats), seems very weak, is vomiting repeatedly, has trouble breathing, appears painful, or if you suspect toxin exposure (especially lilies). Sudden blindness or dilated pupils can also be an emergency due to high blood pressure.

Action steps this week

• Track litter box changes: Bigger clumps and more frequent urination matter.
• Weigh your cat: Even a small monthly loss is worth discussing with your vet.
• Prioritize hydration: Add wet food, consider a cat water fountain, and offer multiple water stations.
• Schedule routine labs: Especially for senior cats, trending values over time is powerful.
• Ask about blood pressure and urine protein: These are common missing pieces in CKD workups.

If your cat has been diagnosed with kidney disease, you are not behind and you are not alone. With a steady plan and the right support, many cats stay bright, comfortable, and affectionate for a long time.