Kidney disease in cats: what are the signs and what can you do?

The kidneys clean the blood. They remove waste through the urine, keep water and salts in balance, help control blood pressure and help make red blood cells. In kidney disease they can no longer do all of that properly.

Chronic kidney disease (CKD) means kidney damage that lasts at least three months. It is permanent: lost kidney tissue does not grow back. It usually gets worse slowly, at a speed that differs a lot from cat to cat. Treatment slows it and keeps the cat comfortable; it does not cure it.

It is one of the most common illnesses of older cats and one of the most common reasons they die. How many cats have it varies a lot between studies. The kidneys have a large reserve: signs usually appear only when roughly two thirds to three quarters of the working kidney tissue is gone. So a cat can have kidney disease for a long time while eating and playing normally.

A healthy cat can manage fine with one kidney. The trouble in CKD is that both kidneys are slowly damaged, usually by scarring and inflammation of the filtering tissue.

Acute kidney injury (AKI) is a sudden drop in kidney function in a cat that was well before. Chronic kidney disease develops slowly over months to years. They look the same in blood tests, so a vet tells them apart from the story, the examination and sometimes an ultrasound.

AKI can come from poisons (lilies, antifreeze, some human painkillers), a blocked bladder or urine flow, severe dehydration, infection or low blood pressure. It is an emergency: the cat can become very ill within days. Unlike CKD, it can sometimes be reversed if treated fast, often with a drip in hospital. Reported survival is around half, so speed matters.

A cat that passes little or no urine can have acute kidney failure or a urinary blockage. Both are emergencies. A cat that recovers from AKI can be left with permanent damage, so the vet keeps an eye on the kidneys afterwards.

Sometimes a sudden flare-up comes on top of existing CKD. It looks like AKI and is often the moment an owner first notices something. Weight loss in the weeks before points to a chronic problem underneath, and the outlook afterwards is more guarded.

Early kidney disease usually shows no signs at all. It is often found by a routine blood and urine test. Drinking and peeing more often appear only later.

The signs owners notice most are drinking more, peeing more (sometimes outside the box), eating less, losing weight, being tired and vomiting. Cats drink more because the kidneys can no longer hold on to water. Other signs are bad breath, a dull or unkempt coat, mouth sores and drooling, from waste building up in the blood, and pale gums from anaemia.

Late in the disease many cats drink less again and just get weak, withdrawn and stop eating. So a cat that does not drink much is not necessarily a cat with healthy kidneys.

High blood pressure is common with kidney disease and often has no visible sign. If it damages the eyes, a cat can go suddenly blind. In very advanced disease the build-up of waste can cause confusion, fits, collapse and coma.

In most cats the exact cause is never found. Age is the only clear, consistent risk factor, and ageing kidneys are the most common background. In one study of healthy cats aged 7 and over, about 13 in 100 developed CKD stage 2 or worse within two years, and each extra year of age raised the risk.

Known causes include kidney infection, tumours such as lymphoma, poisons and drugs, inflammation of the kidney filters, blocked urine flow and inherited disease such as polycystic kidney disease. Treating a cause that can be found can sometimes slow the disease.

Kidney disease can start in younger adult cats too, from about nine months of age, but over half of affected cats are seven or older. In cats over 8, protein in the urine and urine that stays too dilute are early warnings that CKD may follow.

Vets diagnose CKD from the whole picture: the story, an examination, blood tests, urine tests, blood pressure and sometimes imaging. It rests on results that stay abnormal, not on one reading, in a cat that is well hydrated and stable.

Creatinine is a waste product from muscle that healthy kidneys clear. When it rises, the kidneys are filtering less. It only rises after roughly three quarters of kidney function is lost, and it can look normal in a thin cat with little muscle, so a normal creatinine does not rule out kidney disease. SDMA is a newer blood marker that usually rises earlier and is little affected by muscle; in one study a median of 17 months earlier. A high SDMA is checked again after at least two weeks before anyone calls it kidney disease. Urea counts too, but tells less, because diet and dehydration change it.

In the urine the vet looks at how well the kidneys concentrate it. Healthy cats make strong urine; urine that keeps staying dilute suggests a kidney problem. One dilute reading means little. A urine protein test shows whether protein leaks through the kidneys. A bladder infection can spoil the result, so the urine is often cultured first.

Blood pressure is measured with a cuff, painlessly. Blood phosphate, potassium, calcium and red cell count are checked too, and an ultrasound can show the size and shape of the kidneys. Some blood values are most reliable after a fast, because a meat meal raises creatinine; ask whether your cat should come without breakfast. A baseline around age 8, while the cat is healthy, makes later changes easier to read.

Vets describe how far CKD has gone with the IRIS stages: four steps, based mainly on creatinine, with SDMA as an extra. The stage guides treatment, follow-up and how to talk about the outlook. It is used only once CKD is confirmed in a stable, hydrated cat.

Stage 1: waste values are still normal, but something else points to the kidneys, such as persistently dilute urine, protein in the urine or an odd-looking kidney on a scan. Cats usually have no signs. Stage 2: mildly raised waste values. Signs are mild or absent, such as a little more drinking and peeing and now and then less appetite. About a third of kidney function is said to be left.

Stage 3: moderately raised waste values. Many cats now show signs such as weight loss, vomiting and poor appetite, and treatment of those signs usually starts. About a quarter of function is said to be left. Stage 4, the end stage: severely raised values. Cats usually feel unwell: they refuse food, vomit, lose weight quickly and become weak. Care focuses on comfort and on keeping them eating. Less than a tenth of kidney function is left.

As a guide for creatinine: stage 2 is about 140 to 250, stage 3 about 251 to 440 and stage 4 above 440 micromol per litre. Labs use slightly different cut-offs and units, so your report may not match exactly. If creatinine and SDMA point to different stages, both are repeated after a few weeks and the higher stage is used. Each stage is sub-staged by protein in the urine and by blood pressure, because both affect how fast the disease moves. The stage can change and is looked at again at each check.

Vets usually combine a kidney diet, enough water, control of blood phosphate, protein loss and blood pressure, and treatment of symptoms. What happens depends on the stage: in stage 1 mostly monitoring and avoiding anything that harms the kidneys, in stage 2 usually a kidney diet as well, in stages 3 and 4 also treatment of symptoms and complications. The plan is tailored to the cat and adjusted regularly.

High blood pressure is treated with a medicine that widens the blood vessels; amlodipine is what vets most often use in cats. A different group of medicines is commonly used to reduce protein loss in the urine. If phosphate stays high on the diet, a phosphate binder can be mixed into the food. For nausea and poor appetite vets commonly use mirtazapine and maropitant. Anaemia and low potassium can be treated too. The vet chooses each medicine and the amount; this page does not.

Bladder infections are more common in cats with CKD and are often silent. Antibiotics are chosen from a urine culture. Pain relief is part of the care, but it has to suit the kidneys: common anti-inflammatory painkillers (NSAIDs) can harm them. Never give human painkillers.

A cat in a crisis, with a lot of waste in the blood or dehydrated, may need a few days in hospital on a drip. Kidney transplants and dialysis are available only at a few specialist centres, are rarely used in cats and are not a cure. Stem cell therapy and several herbal or probiotic supplements have no clear benefit. Tell the vet if giving medicine is a fight: that is something to bring up, not to put up with.

A kidney diet is the best-supported treatment and usually the first change a vet advises. It limits phosphorus most of all, usually protein and sodium too, and adds omega-3 fatty acids, potassium and B vitamins. In studies, cats on a kidney diet had fewer crises and lived longer than cats on ordinary food.

IRIS suggests a kidney diet from stage 2 and recommends it in stages 3 and 4. In stage 1 the benefit is unclear, except when a lot of protein is lost in the urine. Sooner is not always better: some cats lose muscle when protein is cut too early. Cats need protein, so never cut protein or salt on your own.

Switch slowly. Mix a little new food into the old and build it up over one to several weeks. Do not start a new diet while the cat feels sick; the nausea is treated first. Mixing is fine while changing over, but ordinary food has roughly double the phosphate, so long-term the aim is the kidney diet alone, unless the vet says otherwise.

Eating enough matters more than eating the perfect food. If your cat refuses the kidney diet, keep it eating something and ask the vet. A cat that stops eating gets worse quickly. A small group of cats develop high blood calcium on kidney diets, so the vet follows blood values after a switch.

A cat with CKD loses a lot of water in its urine, so dehydration is always a risk. Put fresh water in several places, try a drinking fountain, change the water at least twice a day, feed wet food rather than only dry and add a little water to wet food. Stock or salt does not belong in it.

How much does a cat with kidney disease drink? There is no fixed daily amount that separates normal from not normal. What counts is a clear increase for your cat compared with before. Tell the vet, who can then check the urine.

Some cats get fluids under the skin, mostly in stages 3 and 4, and sometimes the vet teaches the owner to give them at home. The vet decides if they are needed, how often and which fluid, because too much, or the wrong fluid, can do harm. Blood pressure and protein-loss medicines are not given to a dehydrated cat: hydration comes first.

Poor appetite is one of the biggest problems, partly because waste in the blood causes nausea. A cat that eats too little loses weight and muscle quickly, so ask for help early. If eating stays too low even with medicine, a feeding tube through the nose or the neck can give food, water and medicine. Do not put medicine in the food unless the vet says so: a bitter taste can put the cat off eating.

High blood pressure is reported in roughly 2 to 4 in 10 cats with CKD, and by some sources more. It can damage the eyes, brain, heart and the kidneys themselves. Anaemia affects roughly 3 to 6 in 10; pale gums, tiredness and low appetite are the clues.

Low potassium, high phosphate and an acid blood balance make cats weak, dull the appetite and speed up the disease, which is why bloods are re-checked. Mouth ulcers, nausea, constipation and dehydration can also be painful or unpleasant.

An overactive thyroid, arthritis and silent bladder infections are common in the same age group too. They interact with kidney disease, so they are treated as well.

Polycystic kidney disease (PKD) is an inherited disease in which fluid-filled cysts replace normal kidney tissue. It is mainly seen in Persians and related breeds such as Exotic Shorthairs, Himalayans and British Shorthairs. The cysts are there from birth and grow slowly. Many cats stay well for years; kidney failure usually appears in adult life, often around 7, with a wide spread. Not every cat with PKD gets sick from it.

PKD is dominant: a cat that carries it has a one-in-two chance of passing it on to each kitten. A cheek-swab DNA test finds the main gene change, and in experienced hands ultrasound can show cysts from about 7 weeks old. The gene test shows the gene but not how severe the disease will be. How common PKD is in Persians depends on the study: from about 5 in 100 where breeders had already tested to more than a third elsewhere.

There is no cure; care follows the usual approach for CKD. If you want a Persian-type kitten, ask the breeder for PKD results for both parents. A cat with PKD should not be bred from. Maine Coons, Abyssinians, Siamese, Burmese, Russian Blues and Ragdolls also appear on lists with more kidney disease, but that evidence is older and weaker than for PKD.

Nobody can say for one cat. Many cats with CKD enjoy a good quality of life for months or years, and some barely progress or die of another illness first. The course often goes in steps: a stable period, a crisis, then another plateau.

Numbers from studies are group averages with a huge spread, and they come from older studies. In them, cats diagnosed at stage 2 often lived about one and a half to three years, at stage 3 roughly five months to two years and at stage 4 a few weeks to a few months. Treat that as the spread, not as a forecast for your cat.

What helps the outlook: finding it early, a kidney diet, controlled blood pressure and phosphate, little protein in the urine, a good red cell count and keeping the cat eating and drinking. After a sudden crisis on top of CKD the outlook is more guarded.

In end-stage disease, usually stage 4, the waste in the blood makes a cat feel sick all the time. Care shifts to comfort: fluids, appetising food, anti-sickness and appetite medicine, pain relief and a quiet place. Signs that the end is near include refusing food and water, constant vomiting, rapid weight loss, weakness, hiding, not grooming and, in some cats, fits or collapse.

Putting to sleep is the kind choice when treatment no longer controls the signs or quality of life is poor. There is no number or blood value that sets the day. Look at your cat's life together with the vet: does it still eat and drink, wash itself, move without pain, use the litter tray and show interest in its surroundings? And ask yourself how you are coping.

A diary of good and bad days, with appetite, nausea and pain, helps you and the vet. Several illnesses that can each be treated can still add up to a poor life. Raise end-of-life questions early: it gives you time, and comfort care can be valuable while you decide. You decide together, and you are the one who knows your cat. If the cost of care weighs on you, tell the vet; there may be options.

Kidney disease in older cats cannot always be prevented, but finding it early gives the best chance of a longer, healthier life. Regular check-ups with weight, blood pressure, blood and urine tests are the main tool, more often as a cat gets older. Blood tests before an anaesthetic can double as a kidney check.

Weigh your cat regularly and tell the vet about a weight loss of more than 10 in 100: weight loss is often the first sign. Keep poisons away: lilies, antifreeze and human medicines. Have an overactive thyroid and bladder infections treated too, because they interact with the kidneys.