Kidney Disease in Dogs: Signs, Diet and Management

If your older dog has started drinking far more than usual and topping up the water bowl becomes a daily job, the kidneys are one of the first things a good vet will want to check. Kidney disease is one of the most common serious conditions in senior dogs, and the frustrating part is that it hides in plain sight until a lot of damage is already done. Understanding what the signs mean, and the difference between the sudden and the slow forms, helps you act early, when action matters most.

What the kidneys actually do

The two kidneys are quiet workhorses. They filter waste products out of the blood, balance water and minerals like phosphorus and potassium, help control blood pressure, keep the body's acid levels steady, and release a hormone that tells the bone marrow to make red blood cells. When they start to fail, all of that drifts out of balance at once, which is why a poorly kidney patient can seem unwell in so many different ways.

Here is the catch that surprises most owners: dogs have a large amount of spare kidney capacity. Outward signs usually only appear once roughly two-thirds of working kidney tissue has already been lost. By the time your dog looks ill, the disease has often been building for a while. That is exactly why early screening in older dogs is worth so much.

Acute versus chronic: two very different problems

The single most important thing to get right is which type you are dealing with, because the outlook and the urgency are completely different.

Acute kidney injury (AKI) comes on over hours or days. The kidneys stop working suddenly, often because of a specific insult: a toxin (antifreeze/ethylene glycol is a classic and deadly one, along with grapes, raisins, lilies, and human painkillers such as ibuprofen), a serious infection like leptospirosis, a blockage in the urinary tract, or a sharp drop in blood flow from severe dehydration, heatstroke or shock. AKI is a medical emergency. The upside is that if the dog reaches a vet quickly, some or all kidney function can sometimes be recovered.

Chronic kidney disease (CKD) is the slow version. Damage accumulates over months or years, it cannot be reversed, and it is far more common in older dogs. CKD is managed rather than cured, and with good management many dogs stay comfortable for a long time.

A dog can also have both at once. A stable CKD patient who then eats something toxic or becomes badly dehydrated can suffer an "acute-on-chronic" crisis, where a sudden decline is layered on top of the long-term disease.

| | Acute kidney injury (AKI) | Chronic kidney disease (CKD) | |---|---|---| | Onset | Hours to days | Months to years | | Common triggers | Toxins, infection, blockage, dehydration/shock | Age-related decline, long-standing damage, some inherited conditions | | Reversible? | Sometimes, with fast treatment | No — managed, not cured | | Typical age | Any age | Usually older dogs | | Urgency | Emergency — same-day vet | Ongoing management with monitoring |

Signs to watch for

Early CKD is sneaky. The first thing most owners notice is a change in drinking and toileting.

• Drinking more (polydipsia) and urinating more (polyuria) — often the earliest and most reliable clue. The urine may look pale and watery.
• Reduced appetite and weight loss — picking at food, or going off it altogether.
• Vomiting and nausea — a build-up of waste products (uraemia) upsets the stomach.
• Low energy and a dull, unkempt coat.
• Bad breath with a chemical or ammonia-like smell, and sometimes mouth ulcers.
• Dehydration despite the extra drinking.

Advanced signs, or the sudden signs of acute injury, are more dramatic and need urgent attention.

Get to a vet straight away if your dog stops producing urine (or produces very little), is repeatedly vomiting, becomes suddenly weak or collapses, has seizures, or you know or suspect they have swallowed antifreeze, grapes, raisins or human medication. These can signal acute kidney injury, which is a genuine emergency.

How vets diagnose and stage it

Diagnosis is a vet's job, and it rests on more than one test. From experience, it is worth knowing what the results mean so the conversation in the consulting room makes sense.

• Blood tests measure waste products the kidneys should be clearing: creatinine and urea (BUN), plus phosphorus and potassium. Many UK labs now also run SDMA, a newer marker that can flag trouble earlier — it tends to rise well before creatinine does.
• Urine tests check how well the kidneys concentrate urine (specific gravity), and a urine protein-to-creatinine ratio (UPC) measures protein leaking through the damaged filter. A dipstick and, if infection is suspected, a culture may be added.
• Blood pressure is checked, because kidney disease and high blood pressure feed each other.
• Imaging — ultrasound or X-ray — shows the size and shape of the kidneys and can reveal stones, tumours or structural change.

IRIS staging in plain English

UK vets stage CKD using the International Renal Interest Society (IRIS) system. Staging is based on fasting creatinine measured on at least two occasions in a stable, well-hydrated dog (a single high reading in a dehydrated dog can mislead), then refined by protein loss and blood pressure. It matters because treatment changes with the stage.

| IRIS stage | Blood creatinine (µmol/l) | Roughly (mg/dl) | What it means | |---|---|---|---| | Stage 1 | < 125 | < 1.4 | No build-up of waste yet; disease flagged by other findings (protein in urine, poor concentrating ability, abnormal SDMA or imaging) | | Stage 2 | 125–250 | 1.4–2.8 | Mild; clinical signs often subtle or absent | | Stage 3 | 251–440 | 2.9–5.0 | Moderate; many dogs now show signs | | Stage 4 | > 440 | > 5.0 | Severe; signs usually obvious |

Each stage is then substaged by proteinuria — a UPC below 0.2 is non-proteinuric, 0.2–0.5 borderline, and above 0.5 proteinuric — and by blood pressure, with persistent readings around 160 mmHg and above treated to protect the kidneys, eyes and heart. Proteinuria and high blood pressure both speed the disease up, so both are treated in their own right.

SDMA deserves a special mention. In longitudinal studies it rose above normal on average around 17 months before creatinine did, which is why a vet may act on a raised SDMA even when the standard bloods still look fine.

Diet: the single biggest lever you control

A properly formulated renal diet is the best-evidenced way to slow CKD and keep a dog feeling well. This is not a marketing claim — clinical trials support feeding a phosphorus-reduced (or protein-and-phosphorus-reduced) diet in IRIS stages 2 and 3 to reduce uraemic flare-ups and extend good-quality life. The principles matter more than the brand.

• Reduced phosphorus — the strongest single factor. High blood phosphorus drives the disease forward and makes dogs feel rotten.
• Moderate, high-quality protein — enough to maintain muscle, restricted enough to cut the waste the kidneys must clear. The old idea of slashing protein as low as possible has softened; over-restricting too early can cause muscle wasting.
• Restricted sodium to help manage blood pressure.
• Added omega-3 fatty acids (fish oil), potassium support, and buffering to counter the acidosis that CKD causes.
• High palatability and calorie density, because keeping a nauseous dog eating is half the battle.

Two practical points from real-world experience. First, introduce a renal diet slowly — mix it with the old food over a week or two — because a dog who already feels queasy can form a lasting aversion to a food you present all at once. Second, do not undo the diet with the treats: a single high-phosphorus chew or a scrap of cheese can blow the day's careful balance. Ask your vet for renal-friendly treat options.

Wet renal food also quietly solves the hydration problem, which brings us to the next point. Never start a home-made or shop-bought "kidney" diet without your vet, and be wary of supplements marketed as kidney cures — they are not a substitute for veterinary care.

Keeping your dog hydrated and comfortable

Hydration is everything for a kidney patient, and it is the part you manage day to day.

• Offer wet food or add warm water to meals.
• Provide several water bowls around the house and garden, kept clean and topped up.
• Many dogs drink more from a pet water fountain — moving water is more tempting than a still bowl.
• In more advanced cases your vet may teach you to give subcutaneous fluids at home, which sounds daunting but becomes routine for many owners.

Beyond fluids, management is tailored to the dog: phosphate binders if diet alone does not control phosphorus, blood pressure medication (such as amlodipine), ACE inhibitors or ARBs (like benazepril or telmisartan) to reduce protein loss, anti-nausea and appetite support (such as maropitant), and treatment for the anaemia that can appear later. Gentle, low-stress mental stimulation helps a convalescing dog stay happy — quiet puzzle toys and enrichment are useful on days when a walk is too much.

What to expect: an honest word on prognosis

Outlook depends heavily on the stage at diagnosis and how the dog responds to treatment. A UK primary-care study (VetCompass, Royal Veterinary College) found a median survival of 226 days from diagnosis — but that figure is dragged down by the many dogs only picked up late, when the disease is already advanced. Dogs caught early, at stage 1 or 2, and managed well can live comfortably for a long time. It is genuinely variable, and your own vet, who knows your dog's bloods and response, is the only person who can give a realistic estimate.

Prevention and catching it early

You cannot prevent every case, but you can tilt the odds and buy time.

• Screen senior dogs. For dogs aged seven and over, ask about a yearly (or six-monthly) blood and urine check. Early detection is the whole game with CKD.
• Keep toxins locked away — antifreeze, grapes, raisins, lilies and all human medications, especially ibuprofen and other anti-inflammatories.
• Never give human painkillers. Many are toxic to canine kidneys.
• Keep fresh water available and watch for changes in drinking.
• Look after the teeth — chronic dental infection adds to the body's inflammatory load.
• Vaccinate against leptospirosis if your vet recommends it for your area and lifestyle, as lepto can cause acute kidney injury.

Common mistakes owners make

• Writing off extra drinking as "just old age" instead of getting it checked.
• Stopping the renal diet because the dog "seems fine" — the diet is what is keeping them fine.
• Feeding high-phosphorus treats and table scraps alongside a careful prescription diet.
• Buying online "kidney support" supplements instead of, rather than alongside, proper veterinary care.
• Reaching for human anti-inflammatories to ease an aching senior dog.

Are some dogs more at risk?

Age is the biggest factor, but certain breeds carry a higher or earlier risk, sometimes through inherited kidney conditions. UK sources and studies flag Cocker Spaniels, Cavalier King Charles Spaniels, Bull Terriers, Boxers, West Highland White Terriers and Shar Peis (prone to a form called amyloidosis) among others. A handful of breeds can develop juvenile kidney disease as young dogs. If you own a predisposed breed, it is worth raising early screening with your vet rather than waiting for signs.

The bottom line

Kidney disease is common, serious, and — in its chronic form — permanent, but it is far from hopeless. Learn the early signs, treat sudden severe symptoms as the emergency they are, lean on your vet for diagnosis and staging, and commit to the renal diet and hydration once a plan is in place. Dogs picked up early and managed steadily often carry on enjoying life for a good while yet.

Sources

• PDSA – Chronic kidney disease in dogs
• PDSA – Kidney disease in pets (acute vs chronic)
• IRIS – Staging system for chronic kidney disease
• IRIS – Reassessment of "normal" values (SDMA and early CKD)
• O'Neill et al., VetCompass/RVC – Chronic kidney disease in dogs in UK veterinary practices