Kidney disease in older cats: what the diagnosis means, and the years it still leaves

The vet says "her kidney values are raised", and most owners stop hearing anything after that. It sounds like the beginning of the end. For the majority of cats it is the beginning of a long, manageable chapter: chronic kidney disease found early commonly leaves a cat two, three, often more good years. What decides which side of that a cat falls on is mostly timing and a small number of things done consistently.

This is the companion to our piece on cats that start drinking more water. That one is about noticing. This one is about what happens next.

What is actually going wrong#

A cat's kidneys filter waste out of the blood, hold on to water, balance salts, and help control blood pressure and red-blood-cell production. They are built from hundreds of thousands of tiny filtering units, and those units do not regenerate. Over a long life they are lost, a few at a time, to age, past infections, toxins, high blood pressure, dental disease, genetics and causes nobody ever identifies.

The kidneys have enormous spare capacity, which is both the good and the bad news. A cat feels and looks entirely normal until roughly two-thirds of kidney function is gone. By the time the classic signs appear, more thirst, bigger wet clumps in the tray, weight loss, a poorer coat, picky eating, occasional vomiting, bad breath, the disease has been running silently for a long while.

It cannot be reversed. It can, very often, be slowed to a crawl.

The stages, in plain terms#

Vets worldwide use the IRIS staging system, based mainly on a blood value called creatinine, a newer and earlier marker called SDMA, the urine's concentration and protein content, and blood pressure.

• Stage 1. Blood values still normal, but something is off: dilute urine, protein in the urine, a raised SDMA, or kidneys that look abnormal on a scan. No symptoms. Usually found by luck or by a screening test.
• Stage 2. Mildly raised values. The cat seems fine or drinks a bit more. This is the stage where intervention buys the most time, and the one most often missed because the cat looks well.
• Stage 3. Clearly raised values. Thirst, weight loss and a reduced appetite are typical. Still very treatable; many cats spend years here.
• Stage 4. Severe. The cat feels ill: nausea, not eating, weakness. Treatment now is about comfort and good days.

Average survival figures from the large studies are roughly three years or more from stage 2, around one and a half to two years from stage 3, and weeks to months from stage 4. They are averages, plenty of cats do far better, and the point is the gap between the stages. That gap is the case for finding it early.

The four things that genuinely slow it#

Kidney care is full of supplements and opinions. These four have real evidence behind them.

1. A kidney diet. The single most effective treatment, and the only one shown in controlled trials to lengthen life, roughly doubling survival in stage 2–3 cats in the key study. Prescription renal diets are restricted in phosphate, moderate in high-quality protein, and supplemented with omega-3 and potassium. The phosphate restriction is the part that matters most, because phosphate building up in the blood actively damages what kidney remains.

The practical problem is that cats dislike change. Move over across three to four weeks, mixing a little more each few days. Warm wet food slightly. Try more than one brand and texture; they differ a lot. If a cat flatly refuses, a cat that eats an ordinary food is better off than a cat that starves beside a perfect one, and your vet can add a phosphate binder to the normal food instead.

2. Water, by every route. A kidney cat cannot concentrate urine, so it is always slightly behind on fluid, and dehydration damages kidneys further. Feed wet food. Put out several wide bowls, away from the food and the litter tray. Try a fountain. Add a spoon of water to meals. Later in the disease, many owners learn to give fluids under the skin at home a few times a week. It sounds alarming, takes five minutes, most cats accept it calmly, and it is one of the things that most visibly brings a flat cat back to itself.

3. Blood pressure control. A quarter or more of kidney cats have high blood pressure, which further damages the kidneys and can cause sudden blindness from a detached retina. It gives no warning. It is measured with a small cuff on the leg or tail, and treated with a daily tablet (amlodipine, or telmisartan which also reduces protein loss in the urine). If your cat has kidney disease and nobody has measured its blood pressure, ask.

4. Treating what comes with it. Nausea and poor appetite are treatable (maropitant, mirtazapine as a gel rubbed on the ear). Low potassium, anaemia, urinary infections and protein loss in the urine each have their own treatment. A cat that feels less sick eats, and a cat that eats keeps its muscle and its strength. Much of the difference between a cat that does well and one that fades is whether these smaller problems are picked up and dealt with.

What to avoid#

• Anti-inflammatory painkillers without vet advice. Some can be used carefully in kidney cats; human ones such as ibuprofen never, and paracetamol is fatal to cats at any dose.
• Lilies. Every part of a true lily, including the pollen and the vase water, causes acute kidney failure in cats. They should not be in a house with a cat at all, kidney disease or not.
• High-phosphate treats: cheese, ham, most fish-based and dried-meat treats. If your cat lives for a particular treat, tell your vet and fit it in; do not leave it unmentioned.
• Dehydration: a closed room without water, a missed day of eating, a bout of vomiting left to run. A kidney cat that stops eating for 24 hours needs the vet that day, not a wait-and-see.

Living with it#

Day to day, a kidney cat in stage 2 or 3 is mostly just a cat: the special food, water bowls in odd places, perhaps a tablet in a treat, a check-up every three to six months with bloods, urine and blood pressure.

What helps enormously is a record, because the changes are gradual and memory is unreliable. Four numbers tell most of the story:

• Weight, monthly, on the same scale. Loss of muscle over the spine and hips is an early sign things are moving.
• Appetite, as a simple daily note: all, some, none.
• Water and the litter tray: drinking more, clumps bigger.
• Blood results over time, since the trend matters more than any single value.

Keep them wherever you will actually keep them. The weight log, vet visits and notes on the cat's profile in mypet care are built for this, and being able to show the vet a year of weights on your phone turns a fifteen-minute appointment into a far more useful one.

Finding it before it shows#

The most valuable thing in this article is for owners whose cats are not ill. From the age of about eight, ask for a senior screen once a year: blood including SDMA, a urine sample, and a blood-pressure check. It costs about the price of a good bag of food, and it is the difference between finding kidney disease at stage 2, with years of easy management ahead, and finding it at stage 4 on a Saturday night.

And when the time does come that the good days stop outnumbering the bad, there is a way to think about that too, in our piece on how you know when it's time. For most kidney cats, that is a long way off.