Kidney Disease in Cats: Signs, Stages, and Care

Chronic kidney disease (CKD) is one of the most common health problems in older cats, and it often develops quietly for months or years before an owner notices anything wrong. There is no cure, but early detection through routine senior bloodwork and a vet-directed care plan can slow its progress and help many cats live comfortably for a long time.

This guide is an educational overview, not a diagnosis or a treatment plan. It explains what CKD is, why it shows up so often in senior cats, what early signs can look like, how a veterinarian confirms and stages the disease, and the general categories of care a vet may discuss with you. For the broader picture of caring for an aging cat, see our guide to senior cat care. If your cat is showing possible symptoms, a veterinary visit and bloodwork are the only way to know what is actually going on.

What Chronic Kidney Disease Actually Is

A cat's kidneys filter waste products out of the blood, help regulate hydration and blood pressure, and concentrate urine so the body does not lose too much water. In chronic kidney disease, the kidney tissue is gradually and permanently damaged over time, and the kidneys lose some of their ability to do this filtering and concentrating work. According to the Cornell Feline Health Center, CKD is progressive and, at this time, not reversible, though many cats can still be helped once it is identified.

It helps to separate CKD from acute kidney injury. Acute kidney injury comes on suddenly, often from a toxin, a blockage, or a severe illness, and is a true emergency. CKD, by contrast, is a slow, ongoing loss of kidney function that typically builds up over months to years. A cat can have healthy-looking bloodwork for a long time even as kidney tissue is quietly declining, because a cat's kidneys have a fair amount of reserve capacity before problems become detectable on a standard blood panel.

Why Kidney Disease Is So Common in Older Cats

Age is the single biggest risk factor for feline CKD. Figures shared by Morris Animal Foundation put the rate at roughly 30 percent of cats over the age of 10, and prevalence climbs further in cats in their late teens. International Cat Care notes that CKD can occur at any age but is seen far more often in middle-aged and older cats.

Why cats specifically are so prone to this is not fully settled science, though researchers point to a mix of factors: cats concentrate urine very efficiently for most of their lives, which may put extra long-term strain on kidney tissue, and cumulative wear from years of normal aging, past infections, dental disease, high blood pressure, or other conditions can each contribute to damage that adds up. Because age itself is the main driver, every cat that reaches its senior years is a candidate for screening, not just cats that already look unwell.

Early Signs Owners May Notice

The frustrating part of CKD is that a cat can lose a significant amount of kidney function before any outward sign appears, because the kidneys compensate for a while. When signs do start, they are often subtle and easy to write off as normal aging at first. The most common early clues are increased thirst and increased urination, since failing kidneys become less able to concentrate urine, so the cat drinks more to keep up. A gradual, unexplained drop in weight and a smaller appetite are also frequent early signs, along with a coat that looks a little less kept than it used to.

We cover these two signs in more depth elsewhere, since they overlap with several other conditions and deserve their own explanation: see why is my cat drinking a lot of water and why is my cat losing weight. Neither symptom on its own confirms kidney disease, and both warrant a veterinary visit regardless of the cause, since the list of possibilities for each includes several other conditions that also need attention.

As CKD advances, more noticeable signs can appear, including lethargy, vomiting, bad breath with an ammonia-like odor, poor coat condition, and in some cats, mouth ulcers. How urgently a sign needs attention varies, so the list below is a general guide, not a substitute for a vet visit.

• Increased thirst and urination (emptying the water bowl faster, more or larger clumps in the litter box): book a routine visit within the next 1 to 2 weeks.
• Gradual weight loss (ribs or spine easier to feel, a looser-fitting collar): book a routine visit, sooner if the loss is rapid.
• Reduced appetite (sniffing food then walking away, eating less at each meal): call within a few days; same day if the cat has not eaten at all in 24 hours.
• Lethargy or hiding more than usual: call within a few days.
• Vomiting or bad breath with an ammonia-like smell: call promptly, same day if vomiting is frequent or the cat seems weak.
• Sudden collapse, a full 24 hours without eating, or a male cat straining in the litter box with little or no urine coming out: this is an emergency, go to a vet or emergency clinic immediately.

That last item deserves emphasis: a male cat straining to urinate with little or nothing coming out can be a urinary blockage, which is unrelated to CKD but is a true emergency that can be fatal within a day or two if untreated. When in doubt about how urgent a symptom is, calling your vet's office or an emergency line to describe it is always the safer move.

How Vets Diagnose Kidney Disease

Because CKD is largely invisible on the outside until it is fairly advanced, diagnosis relies on lab testing rather than a visual exam alone. A typical workup that your vet may run includes a blood chemistry panel looking at creatinine and blood urea nitrogen (BUN), both waste products the kidneys normally clear, along with SDMA (symmetric dimethylarginine), a newer marker that can rise earlier than creatinine in some cats. Your vet will also usually request a urinalysis to check urine concentration (called specific gravity), since kidneys that cannot concentrate urine well produce dilute urine even when blood values still look borderline.

International Cat Care notes that vets look at blood and urine together because dilute urine alongside even mildly elevated creatinine or BUN points more clearly toward reduced kidney function than either test on its own. Additional testing your vet may recommend can include blood pressure measurement, since CKD and high blood pressure often occur together, and a urine protein to creatinine ratio, which checks whether the kidneys are leaking protein. Imaging such as an ultrasound is sometimes used to look at kidney size and structure, particularly if your vet suspects a specific underlying cause.

Because early CKD produces no outward signs, many vets recommend baseline senior bloodwork starting well before a cat looks sick, so that later results can be compared against a healthy starting point. To see how often that kind of screening is generally recommended as a cat ages, read our guide on how often you should take a cat to the vet.

How Vets Stage Kidney Disease

Once CKD is confirmed, many vets use a staging framework from the International Renal Interest Society (IRIS) to describe roughly how far the disease has progressed and to help guide the conversation about next steps. IRIS staging is based mainly on blood creatinine and SDMA levels in a stable, well-hydrated cat, and it is then further refined based on whether protein is present in the urine and whether blood pressure is elevated. It is a communication and planning tool for your vet, not a fixed treatment recipe, and your vet is the one who interprets where your individual cat falls and what that means for your cat specifically.

In very general terms, vets stage CKD roughly like this, moving from the earliest, mildest stage toward more advanced disease:

Stages are also modified by whether a cat has protein loss in the urine or high blood pressure, both of which your vet will factor into the overall picture and any plan going forward. Because staging depends on lab values interpreted in context, do not try to stage your own cat from symptoms or a single number, ask your vet to walk you through what your cat's results mean.

General Categories of Management a Vet May Use

There is currently no cure for CKD, but a vet-directed plan can often slow progression and keep a cat feeling better for longer. The specific plan depends heavily on your cat's stage, bloodwork, and any complications, so this section describes general categories only, not a protocol to follow at home. Your own veterinarian decides what, if anything, applies to your cat.

• Diet. A vet may recommend a therapeutic kidney diet formulated to reduce the workload on the kidneys. Whether and when to switch, and which diet, is a decision your vet makes with you based on your cat's specific stage and bloodwork, not something to choose on your own.
• Hydration support. Because failing kidneys struggle to conserve water, a vet may discuss ways to encourage more water intake, and in some cases may recommend fluid therapy that a vet or trained caregiver administers.
• Managing complications. A vet may monitor and treat related issues such as high blood pressure, low potassium, anemia, or excess phosphorus, each with its own vet-directed approach.
• Supplements. Some vets discuss supplements such as omega-3 fatty acids or phosphate binders as part of a broader plan; these are used under vet guidance and are not a cure on their own.
• Monitoring. Regular recheck bloodwork and urine testing, on a schedule your vet sets, tracks whether the disease is stable or progressing and whether the plan needs adjusting.

The VCA Animal Hospitals overview of chronic kidney disease describes how these categories are typically combined and adjusted over time as a cat's needs change, which is one reason ongoing veterinary involvement matters more than any single fix. If your cat's diet needs adjusting for reasons beyond a CKD diagnosis, such as general senior nutrition, see our guide to what to feed a senior cat, though remember that a confirmed CKD diagnosis moves diet decisions into vet-directed territory.

Questions Worth Asking Your Vet

Walking into a kidney disease conversation with a short list of questions can make the appointment more useful and less overwhelming. Consider asking your vet what stage your cat's bloodwork suggests and how confident that reading is, whether repeat testing is needed to confirm a trend before drawing conclusions, and what specific values (such as creatinine, SDMA, or urine concentration) will be tracked over time. It is also reasonable to ask whether your cat's blood pressure or urine protein has been checked, since both change what a management plan might look like, and to ask how often rechecks should happen going forward.

If diet, hydration support, or supplements come up, ask your vet to explain the reasoning in plain terms and what signs would tell you the plan is working or not working. Finally, ask what symptoms, if they appear at home, should prompt an earlier call rather than waiting for the next scheduled recheck. Bringing a written log of your cat's water intake, appetite, and weight to appointments can also help your vet spot trends faster than memory alone.

Frequently asked questions