Signs of kidney disease in cats

Kidney disease is one of the most common things a cat is diagnosed with in its later years, and one of the hardest to catch by eye, because cats lose kidney function gradually and hide the early stages well. Most owners do not notice anything is wrong until a fairly ordinary vet visit turns up unexpected bloodwork, or until a change becomes too obvious to miss. Here is what actually shows up, in roughly the order it tends to appear, and why acting on the early signs matters so much more than the late ones.

The kidneys’ job, and why cats lose it so often

A cat’s kidneys filter waste out of the blood, balance salts and fluid, and control how concentrated urine is. Chronic kidney disease means that filtering tissue has been damaged, usually slowly over months or years, and does not regenerate once it is gone. Cats are unusually prone to this compared with dogs, and nobody has one single answer why, though age, genetics, past dehydration, and infections all seem to play a part. What matters practically is that a cat can lose a large share of kidney function, well over half in some cases, before bloodwork looks clearly abnormal, which is exactly why the outward signs described below are worth acting on early rather than waiting for a diagnosis to confirm what you already suspect.

The early signs: drinking and urinating more

The pairing owners notice first, and the one worth taking seriously, is a cat drinking more than it used to and producing more urine.

Failing kidneys lose the ability to concentrate urine properly, so the body flushes out more water than it should, which drives thirst up to compensate. In practice this looks like a water bowl that empties faster than before, a cat drinking from taps or unusual places more than it used to, and litter clumps that are noticeably larger or more frequent than normal. It is easy to miss at first, since it happens gradually, and easy to write off as a hot spell or a diet change. A genuine, sustained increase in either drinking or urination in an older cat is worth a vet visit on its own, before any other sign has appeared.

The signs that show up as it progresses

As kidney function drops further, the signs become harder to miss, and this is the stage most owners associate with “kidney disease” without realising milder signs came earlier.

Weight loss and a smaller appetite are common, sometimes alongside a coat that looks duller or less well groomed, since a cat that feels unwell grooms itself less. Bad breath with a distinct ammonia-like or chemical smell can develop as waste products build up in the blood, and some cats vomit occasionally or seem nauseous, particularly in the mornings. Lethargy and general quietness tend to creep in alongside these, a cat sleeping more and showing less interest in things it used to enjoy. Our piece on why is my cat losing weight goes into the wider list of causes weight loss can point to, kidney disease being one of the more common ones in an older cat.

How it gets diagnosed

Because the early signs are easy to dismiss, diagnosis usually comes from bloodwork rather than symptoms alone, which is why routine senior checks matter even in a cat that seems fine.

A vet will typically run blood tests looking at creatinine and an SDMA level, alongside a urine sample to see how well the kidneys are still concentrating it. SDMA can flag reduced kidney function earlier than creatinine used to catch it alone, sometimes while a meaningful amount of function is still working, which gives more time to act before things progress. Blood pressure is usually checked too, since high blood pressure often travels alongside kidney disease in cats and can silently damage the eyes and other organs if it goes unnoticed. Vets typically stage the disease from these results, which shapes how aggressively it needs managing.

What management actually looks like

There is no cure, since damaged kidney tissue does not come back, but chronic kidney disease is genuinely manageable, and plenty of cats live comfortably for years after diagnosis with the right care.

A prescription kidney-support diet, lower in phosphorus and adjusted in protein, is usually the single biggest lever, and most cats need a vet-guided food rather than an over-the-counter choice. Keeping water intake up matters just as much here as it does for a healthy cat, so a fountain-style water source, wet food, and water added to meals are all worth trying, alongside the same approach in our guide to getting your cat to drink more water. For cats further along, vets sometimes teach owners to give fluids under the skin at home, which sounds daunting at first but becomes routine quickly and can make a real difference to how a cat feels day to day. Regular monitoring, usually every three to six months once diagnosed, tracks how things are progressing and lets the plan adjust as needed.

Kidney disease is common enough in older cats that routine bloodwork from around age ten, even in a cat that seems completely well, is one of the more genuinely useful things you can do for a senior cat. Watch for a water bowl that empties faster than it used to, and treat that alone as a reason to get bloodwork done rather than waiting for weight loss or a duller coat to confirm it. Our guide to caring for a senior cat covers the wider pattern of checks worth building into an older cat’s routine.