A cat can lose a huge chunk of kidney function before anything looks obviously wrong. By the time the classic symptoms show up, vets are often already looking at a cat who has quietly been in early-stage kidney disease for a year or more. That's the frustrating part of feline chronic kidney disease (CKD): it's common, it's manageable if caught early, and it's also very good at hiding.
Here are five signs that genuinely warrant a vet visit and bloodwork, not just a "let's keep an eye on it."
1. Drinking more, peeing more
This is usually the first thing owners notice, and it's easy to dismiss because a cat drinking from the tap or hovering by the water bowl doesn't look like a medical emergency. But increased thirst and increased urination, often described together as polyuria and polydipsia, show up when the kidneys start losing their ability to concentrate urine properly. Instead of retaining water efficiently, the kidneys let too much go, so the cat compensates by drinking more.
Watch for a litter box that needs scooping more often, noticeably larger urine clumps, or a water bowl that empties faster than it used to. Some owners only notice this in hindsight, after a vet asks the question directly and they realize they'd been refilling the bowl an extra time a day without really registering it.
2. Losing weight while eating normally
Weight loss with a normal or even increased appetite is one of the more counterintuitive signs, and it trips people up because "she's still eating fine" feels like reassurance. It isn't, necessarily. Cats in the early-to-middle stages of CKD can eat a full portion and still lose muscle and body condition, partly because the kidneys are working harder to do less, and partly because toxin buildup in the blood affects metabolism generally.
Run a hand along the spine and hips every few weeks, especially with senior cats. A cat who felt padded in spring and feels bony by autumn has lost weight regardless of what the bowl says. This is one of those areas where a scale at home, checked monthly, catches things that eyeballing in passing will miss.
3. A coat that's stopped looking cared for
Grooming is one of the first behaviours to slip when a cat isn't feeling well, and kidney disease is a common, under-recognised cause of it. A cat with early CKD may simply feel a bit off, a bit nauseated, a bit less inclined to spend twenty minutes a day working through its coat. The result is fur that looks greasy, flat, or slightly matted along the back and hindquarters, areas a cat would normally reach easily.
People often chalk this up to age alone, and age is part of it. But an unkempt coat in a cat that used to groom meticulously is worth mentioning at the next appointment, not filing away as "just getting older." It's a genuinely useful early clue, and one that's easy to photograph over a few weeks if you want to show your vet the change rather than describe it.
4. Appetite that comes and goes, or bad breath
Where sign two is about weight loss with steady eating, this one is about the eating itself changing. As kidney disease advances, waste products that the kidneys would normally filter out start building up in the blood, a state called uremia. This can cause nausea, mouth ulcers, and a distinctive ammonia-like smell on the breath. Cats may sniff at food and walk away, eat half a portion and stop, or go through a few days of reduced interest in food followed by a few days of eating normally.
This is also where people commonly go wrong: they assume a fussy few days means the cat is bored with its food and switch brands repeatedly, when actually the fluctuating appetite is the symptom, not a preference issue. If a cat's appetite has become genuinely unpredictable over several weeks, that pattern itself is the thing to report, not just "she didn't eat today."
5. Lower energy and a shift in personality
This one is vaguer and harder to pin down, which is exactly why it gets missed. A cat that used to greet you at the door and now waits on the sofa. A cat that slept nine hours a day and now sleeps twelve. A normally social cat that starts avoiding the family room. None of this points specifically at kidneys on its own, but combined with any of the four signs above, it rounds out a picture that's worth acting on rather than watching indefinitely.
Lethargy in CKD relates back to the same uremic toxin buildup that affects appetite, plus mild anemia, which is common as kidney disease progresses and the kidneys produce less of the hormone that stimulates red blood cell production. A cat running on fewer red blood cells is, understandably, a cat with less get-up-and-go.
What kidney testing actually involves
A vet suspecting CKD will usually run a blood chemistry panel and a urinalysis together, since neither test alone tells the full story. Blood work typically checks creatinine and BUN, older markers that only rise once a meaningful chunk of kidney function is already gone, alongside SDMA, a newer marker that tends to increase earlier in the disease process. Urine testing checks how concentrated the urine is and screens for protein loss, both of which help confirm what the bloodwork is suggesting. Blood pressure is often checked too, since hypertension and kidney disease frequently travel together in cats.
One abnormal result usually isn't enough for a diagnosis. Vets generally want to see a pattern hold over a repeat test, often a few weeks to a few months apart, before staging the disease and building a treatment plan around it.
| Sign | What's actually happening | How urgent |
|---|---|---|
| Increased thirst and urination | Kidneys losing ability to concentrate urine | Book a check-up within the next couple of weeks |
| Weight loss with normal appetite | Reduced kidney efficiency, altered metabolism | Same, sooner if weight loss is rapid |
| Unkempt or greasy coat | Reduced grooming due to feeling unwell | Worth mentioning at next visit |
| Inconsistent appetite, bad breath | Toxin buildup (uremia) affecting nausea | Book sooner if breath smells distinctly off |
| Lethargy, behaviour changes | Uremia plus possible mild anemia | Combine with other signs to judge urgency |
At Cat Wonder, we hear from a lot of owners who assumed these changes were "just old age." Sometimes that's true. But age is a risk factor for kidney disease, not a diagnosis in itself, and the two get conflated constantly. If you're already tracking your cat's twice-yearly senior checkups, ask specifically for kidney values to be flagged on the report rather than just reviewed as "normal" or "abnormal" in passing.
Where owners tend to go wrong
The most common mistake is waiting for more than one symptom before acting, or waiting for the symptoms to feel severe. CKD doesn't announce itself. A cat drinking slightly more water for three months is a stronger early signal than a cat who suddenly stops eating altogether, and yet the dramatic version is what usually gets someone to the vet. If you've noticed even one of the five signs above holding steady for a couple of weeks, that's reason enough to ask for bloodwork, not a reason to wait and see if it gets worse.
The second common mistake is treating sudden appetite loss as a food problem and cycling through brands before mentioning it to a vet. It delays the actual diagnosis by weeks, sometimes months, while the cat's condition quietly progresses.
Cats are also masters at hiding discomfort generally, something covered in more detail in our piece on signs of pain cats try hard to hide, and kidney disease follows the same pattern. There's rarely a dramatic moment. There's a slow drift, and the drift is the thing to catch.
A note on senior cats specifically
CKD is disproportionately a disease of older cats, and prevalence climbs sharply from around age ten onward. This is part of why blood and urine screening as a routine part of senior wellness visits matters so much, catching a rising SDMA value before a cat shows any symptoms at all gives a genuine head start on management, whereas waiting for symptoms usually means a fair amount of kidney function is already gone. Diet changes, phosphorus management, and blood pressure control all work better the earlier they start.
If your cat is younger and otherwise healthy, none of this is cause for alarm on its own. But if you're noticing any combination of the five signs above, particularly in a cat over seven or eight, it's a reasonable and low-drama thing to ask your vet to check.
FAQs
Can kidney disease in cats be cured? No, chronic kidney disease isn't reversible, since the kidney tissue that's already damaged doesn't regenerate. It can, however, be managed well with diet changes, medication, and monitoring, and many cats live comfortably for years after an early diagnosis.
Is increased thirst always a kidney problem? Not always. Diabetes and an overactive thyroid can also cause a cat to drink and urinate more, which is exactly why a vet will usually run a fuller panel rather than assuming kidneys are the cause from thirst alone.
How often should older cats get kidney bloodwork? Most vets recommend annual screening from around age seven, moving to twice yearly from around ten or eleven, since kidney values can shift meaningfully within six months in a cat already showing early changes.
Does wet food help protect a cat's kidneys? Wet food supports better overall hydration than dry food alone, which is generally helpful, but it isn't a substitute for testing or treatment once kidney disease is actually present. A prescription renal diet, if your vet recommends one, is formulated specifically around reduced phosphorus and controlled protein quality.
My cat's bloodwork came back borderline. What now? Borderline results usually mean a repeat test in a few weeks to a few months, watching for a trend rather than reacting to a single number. A one-off borderline creatinine or SDMA reading isn't a diagnosis on its own.
If you want to read more on what a good senior wellness visit should actually cover, our guide on what twice-yearly cat exams catch early goes through it in more detail.
