Chronic Kidney Disease in Cats: Early Signs, Diet, and Living Well With a CKD Diagnosis

If you share your home with a cat aged ten or older, chronic kidney disease (CKD) is one of the most important conditions to understand. It is among the leading causes of illness and death in senior cats — studies suggest roughly one in three cats over the age of ten is affected to some degree. The hard part is that CKD is quiet. By the time most owners notice something is wrong, the kidneys have often lost a large share of their function. The good news is that CKD is rarely a sudden crisis: it usually progresses slowly, and with early detection and steady management, many cats live comfortably for months or even years after diagnosis.

A practising vet walks through what kidney disease in cats is, how it's diagnosed, and what owners can do.

What the Kidneys Do — and What "Chronic" Means

The kidneys are remarkable filtering organs. They clear waste products from the blood, balance water and electrolytes, control blood pressure, regulate the body's acid balance, and produce a hormone that tells the bone marrow to make red blood cells. Each kidney is built from thousands of microscopic filtering units called nephrons. Cats are born with a fixed number, and once a nephron is lost, it does not regenerate.

"Chronic" kidney disease means this loss happens gradually, over months or years, as opposed to acute kidney injury, which comes on suddenly (often from a toxin such as lilies or antifreeze, a urinary blockage, or infection). Because cats have so much spare kidney capacity, the body compensates beautifully at first. Outward signs typically don't appear until around two-thirds of kidney function has already been lost — which is exactly why CKD is so easy to miss in its early stages, and why routine senior blood work matters so much.

The Early Warning Signs Owners Miss

The earliest and most reliable clue is a change in drinking and urinating. A damaged kidney can no longer concentrate urine efficiently, so the cat produces larger volumes of dilute urine and drinks more to keep up. The medical terms are polyuria (increased urination) and polydipsia (increased thirst), often shortened to PU/PD.

In practice you might notice:

• Heavier, more frequent litter clumps, or a cat that starts drinking from taps, glasses, plant pots or the shower.
• Gradual weight loss, especially loss of muscle over the spine and hips, even while the appetite still seems normal.
• A duller, unkempt coat and reduced grooming.
• Lower energy — more sleeping, less play, a generally "old" demeanour that's easy to write off as just ageing.

As the disease advances, toxins (chiefly urea) build up in the blood — a state called uraemia — and cats may develop nausea, bad "ammonia" breath, poor appetite, vomiting, mouth ulcers, and constipation from dehydration. Two common complications add to the picture: high blood pressure, which can damage the eyes and cause sudden blindness, and anaemia, because failing kidneys make less of the hormone that drives red blood cell production. None of these later signs should be waited for — the goal is to catch CKD long before they appear.

How CKD Is Diagnosed

Diagnosis combines blood and urine tests. On bloodwork, vets look at creatinine and urea (BUN), the classic waste markers, and increasingly at SDMA, a newer, more sensitive marker that can flag kidney decline earlier — sometimes when only about 40% of function has been lost, rather than the 65–75% needed before creatinine rises. A urinalysis is essential: dilute urine (a low "specific gravity") alongside raised blood markers is the hallmark of CKD, and the test also checks for protein loss and urinary infection.

Vets stage CKD from 1 (earliest) to 4 (most advanced) using the international IRIS system, which combines creatinine and SDMA levels with blood pressure and urine protein. Staging matters because it guides treatment and gives you a realistic sense of what to expect.

A vet explains the causes, staging and treatment of feline CKD in plain language.

Diet: The Single Most Powerful Tool

If there is one intervention proven to extend both the length and quality of life in cats with CKD, it is a therapeutic kidney diet. Clinical studies have shown these diets can roughly double survival time compared with a standard diet in cats with established disease. They work on several fronts at once:

• Reduced phosphorus — the most important change. High blood phosphorus accelerates kidney damage, so controlling it slows the disease.
• Moderately reduced, high-quality protein — enough to maintain muscle, but tailored to lower the waste load the kidneys must clear.
• Added omega-3 fatty acids from fish oil, which support blood flow within the kidney.
• Added potassium and buffers to counter the potassium loss and acid build-up that CKD cats are prone to.

A few practical points. First, don't switch diets the moment you hear the word "kidney." In very early disease your vet may advise simply controlling phosphorus and monitoring; therapeutic diets are most clearly beneficial from around IRIS stage 2 onward. Second, transition slowly over one to two weeks, mixing increasing amounts of the new food in with the old — cats are famously neophobic, and a CKD cat that stops eating altogether is a bigger immediate problem than the diet itself. Offer wet versions, warm the food slightly to release aroma, and try more than one brand if the first is refused. The best kidney diet is ultimately the one your cat will actually eat.

Hydration and Subcutaneous Fluids

Because their kidneys waste water, most CKD cats are chronically a little dehydrated, which makes them feel worse and stresses the kidneys further. Encouraging water intake is therefore a daily priority:

• Feed wet food wherever possible — it can supply several times more water than kibble.
• Offer a pet water fountain; many cats drink far more from moving water.
• Place several water bowls around the home, away from food and the litter box, and keep them topped up with fresh water.
• Some cats will take a little low-sodium broth or tuna water to boost intake.

In more advanced disease, drinking alone isn't enough, and many cats benefit from subcutaneous (under-the-skin) fluids. This sounds daunting but is something a great many owners learn to do calmly at home, a few times a week, with their vet's guidance — surveys find the large majority of owners and cats tolerate it well. It can make a real difference to how a CKD cat feels day to day.

A feline vet demonstrates the cat-friendly way to give subcutaneous fluids at home.

Medications and Other Treatments

There is no cure for CKD, so treatment aims to slow progression and keep the cat comfortable. Depending on the individual, your vet may add:

• Phosphate binders, mixed into food, when diet alone can't keep phosphorus in range.
• Blood pressure medication (such as amlodipine) if hypertension is found — untreated, it threatens the eyes, heart and brain.
• Anti-protein-loss drugs (ACE inhibitors or telmisartan) when the urine shows significant protein leakage, which is linked to faster decline.
• Anti-nausea and appetite-support medication to keep the cat eating — maintaining food intake is one of the strongest predictors of doing well.
• Potassium supplements and, in later stages, treatment for anaemia.

Just as important is regular rechecking. Most CKD cats are reassessed every three to six months (more often when newly diagnosed or unstable) so treatment can be adjusted as the picture changes.

Living Well With a CKD Cat

A CKD diagnosis is frightening to hear, but it is not the emergency it sounds like. Caught early, it is a condition you manage rather than a countdown. Many cats diagnosed in the earlier stages live happily for years, doing all the ordinary cat things, on nothing more than the right food, good hydration and routine monitoring.

The most useful thing you can do is be the early-warning system the disease relies on you to be. Ask your vet about senior wellness screening — a simple blood and urine panel — from around seven years of age, and yearly or twice-yearly thereafter. Keep a quiet eye on the water bowl and the litter tray, weigh your cat now and then, and flag changes in appetite or energy promptly. Spotting CKD before your cat ever looks sick is the single biggest favour you can do them.

This article is general information, not veterinary advice. Increased thirst, weight loss or appetite changes always warrant a proper veterinary work-up — and if your cat is straining to urinate, producing little or no urine, or has stopped eating, treat it as an emergency and call your vet straight away.