Kidney Disease in Dogs and Cats: IRIS Stages, Symptoms, Renal Diet and Treatment

Short answer: kidney disease is one of the most common serious illnesses of older pets, especially cats. It can be acute (sudden, from poisons or infections such as leptospirosis or tick fever, and sometimes reversible) or chronic (slow, permanent loss of function). Early signs are drinking and urinating more, then weight loss, poor appetite, vomiting and bad breath. Blood tests (creatinine and SDMA), urine tests and blood pressure measurement allow vets to stage chronic kidney disease (CKD) using the IRIS system. A kidney diet, hydration support and treating complications can keep many pets comfortable for years.

Key takeaways

• The kidneys filter waste, balance water and minerals (phosphorus, potassium, sodium), control blood pressure and make erythropoietin, the hormone that drives red blood cell production.
• About two-thirds of kidney function is lost before signs appear, so routine annual blood and urine tests in pets over 7 years old catch it earlier.
• IRIS staging (stages 1–4) uses creatinine and SDMA, then protein in the urine and blood pressure, to guide treatment.
• A veterinary kidney diet (restricted phosphorus, moderate high-quality protein, omega-3s) is the single most proven treatment for prolonging life in CKD.

What the kidneys do

• Filter blood through about 400,000 nephrons per kidney in dogs (around 200,000 in cats), removing urea, creatinine and other toxins
• Concentrate urine to conserve water; loss of this ability is why thirst and urination increase early in CKD
• Balance minerals: phosphorus, potassium, sodium, calcium
• Control blood pressure (renin–angiotensin system)
• Make erythropoietin (red blood cell production) and activate vitamin D

Acute kidney injury vs chronic kidney disease

Signs of chronic kidney disease

• Drinking more water and urinating more (often the first sign); urinating at night or in the house
• Gradual weight and muscle loss, especially over the back and hips
• Reduced or picky appetite; nausea, drooling, lip-licking
• Vomiting, sometimes with blood
• Ammonia-smelling breath; mouth ulcers (uraemic stomatitis)
• Dull, unkempt coat; lethargy
• Pale gums (anaemia)
• Constipation and dehydration (common in cats)
• Sudden blindness from high blood pressure (retinal detachment), especially in cats

How vets diagnose and stage kidney disease

• Blood creatinine and urea (BUN): rise when function is reduced. Creatinine is also affected by muscle mass, so it can underestimate disease in thin pets.
• SDMA: a newer marker that rises earlier, when about 25–40% of function is lost, and is not affected by muscle.
• Urinalysis: urine specific gravity (inability to concentrate), protein, sediment and infection.
• Urine protein:creatinine ratio (UPC): measures protein leaking through damaged filters.
• Blood pressure (Doppler).
• Phosphorus, potassium, calcium, CBC (anaemia).
• Ultrasound and X-rays: kidney size and shape, stones, cysts, blockage.
• Leptospirosis and tick-borne disease tests for suspected AKI.

IRIS staging of CKD (stable patients)

Substaging refines treatment:

• Proteinuria (UPC): non-proteinuric below 0.2; borderline 0.2–0.5 in dogs (0.2–0.4 in cats); proteinuric above 0.5 in dogs (above 0.4 in cats).
• Systolic blood pressure: normal below 140 mmHg; pre-hypertensive 140–159; hypertensive 160–179; severely hypertensive 180 or above (high risk of eye, brain, heart and further kidney damage).

Treatment of chronic kidney disease

1. Kidney (renal) diet

Veterinary renal diets (for example Hill’s k/d, Royal Canin Renal, Purina NF and others available in India) restrict phosphorus, provide moderate amounts of high-quality protein, add omega-3 fatty acids and antioxidants, and are less acid-forming. In cats, studies show they roughly double survival time and reduce uraemic crises. Start from IRIS stage 2 (sometimes late stage 1), and switch gradually over 2–3 weeks. Warming wet food helps appetite.

Home-cooked kidney diets need a vet-formulated recipe, because most home diets are too high in phosphorus (bones, organ meat, paneer, milk, fish with bones) or deficient in essential nutrients. Egg white, white rice and well-cooked chicken breast are commonly used low-phosphorus ingredients, but they must be balanced with calcium and vitamins under guidance.

2. Phosphate control

If blood phosphorus stays high on diet alone, vets add an intestinal phosphate binder (aluminium hydroxide, calcium carbonate or lanthanum) mixed into each meal. IRIS targets: stage 2: 2.7–4.6 mg/dL; stage 3: 2.7–5.0 mg/dL; stage 4: 2.7–6.0 mg/dL.

3. Hydration

• Always provide fresh water; never restrict it.
• Wet food, water fountains and extra bowls, especially in Indian summers.
• Subcutaneous fluids at home (for example 75–150 ml for a cat every 1–3 days, as prescribed), taught by your vet, for dehydrated stage 3–4 patients.

4. Blood pressure and protein loss

• Amlodipine (cats: usually 0.625–1.25 mg per cat once daily; dogs: 0.1–0.5 mg/kg once daily) for hypertension.
• Telmisartan (cats: 1 mg/kg once daily for proteinuria, 2 mg/kg for hypertension; dogs: 1 mg/kg) or benazepril/enalapril (0.25–0.5 mg/kg once or twice daily) to reduce urine protein loss, once the patient is stable and hydrated.
• Recheck blood pressure, creatinine and potassium 1–2 weeks after starting.

5. Nausea, appetite and stomach

• Anti-nausea drugs: maropitant, ondansetron
• Appetite stimulants: mirtazapine (oral or transdermal gel for cats), capromorelin where available
• Antacids (famotidine, omeprazole) if stomach ulceration is suspected

6. Other complications

• Low potassium (common in cats): potassium gluconate supplements.
• Anaemia: iron, and darbepoetin or erythropoietin injections when PCV falls significantly.
• Metabolic acidosis: potassium citrate or sodium bicarbonate.
• Urinary tract infections: urine culture at least yearly.
• Omega-3 fatty acids (fish oil) support kidney blood flow.

Treatment of acute kidney injury

AKI needs hospital care: IV fluids with careful monitoring of urine output, correcting potassium and acid–base balance, anti-nausea drugs, treating the cause (antibiotics such as doxycycline for leptospirosis, antidotes or decontamination for poisons), and, in referral centres, dialysis for pets that stop producing urine. Some pets recover fully; others are left with CKD.

Monitoring and outlook

Many cats live for years after diagnosis, especially when CKD is found at stage 2 and treated. Published median survival for cats is roughly 3 years at stage 2, 2 years at stage 3, and around 3 months at stage 4. Dogs often progress faster, particularly with significant protein loss in the urine.

Prevention

• Annual blood and urine tests from age 7 (yearly for cats from 7; every 6 months for seniors).
• Never give human painkillers. See paracetamol and pets.
• Keep grapes and raisins away from dogs and lilies away from cats. See can dogs eat grapes.
• Vaccinate dogs against leptospirosis and control rats, especially in monsoon and flood-prone areas.
• Year-round tick control. See tick fever in dogs.
• Treat dental disease (see dog dental disease), and keep pets well hydrated in Indian summers.

Frequently asked questions

When to call a vet

Book a check for increased thirst or urination, weight loss or poor appetite in older pets. Go immediately for sudden vomiting with weakness, very little urine, suspected poisoning (grapes, lilies, painkillers), sudden blindness, or a pet with known CKD that stops eating.

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• Heartworm in Dogs and Cats in India: Life Cycle, Stages, Tests, Treatment and Prevention
• Giardia and Coccidia in Dogs and Cats: Symptoms, Stool Tests, Treatment and Stopping Re-infection
• Senior Dog Drinking Too Much Water and Peeing a Lot? Diabetes, Cushing’s and Steroid Side Effects
• Parvo in Dogs and Puppies: Stages, Treatment, Recovery Diet and Home Care (Day by Day)

References

• International Renal Interest Society (IRIS). IRIS Staging of CKD (modified 2023) and Treatment Recommendations for CKD in Dogs and Cats.
• Ross SJ, et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. J Am Vet Med Assoc 2006;229:949–957.
• Boyd LM, et al. Survival in cats with naturally occurring chronic kidney disease (2000–2002). J Vet Intern Med 2008;22:1111–1117.
• Acierno MJ, et al. ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. J Vet Intern Med 2018.
• Sykes JE, et al. 2023 Updated ACVIM consensus statement on leptospirosis in dogs. J Vet Intern Med 2023.