Chronic Kidney Disease in Senior Cats
Chronic kidney disease (CKD) is the most common serious illness affecting cats in their senior years. Around one in three cats over the age of twelve will develop CKD, and the condition is responsible for a significant proportion of feline deaths in old age. The kidneys perform essential functions — filtering waste products from the blood, regulating electrolytes, maintaining fluid balance, producing erythropoietin (which stimulates red blood cell production) and activating vitamin D — meaning their progressive loss of function has wide-ranging consequences throughout the body.
Encouragingly, CKD in cats can often be managed effectively for months to years with appropriate diet, hydration support and targeted medication. The WSAVA and IRIS guidelines provide a clear, evidence-based framework for staging and managing the disease, and early intervention consistently produces the best outcomes.
IRIS CKD Staging
The International Renal Interest Society (IRIS) staging system is the globally recognised standard for classifying CKD severity in cats and dogs. It divides CKD into four stages based on fasting plasma creatinine concentration and symmetric dimethylarginine (SDMA) levels, with further sub-staging based on urine protein:creatinine ratio and blood pressure.
- Stage I: Creatinine below 140 µmol/L (SDMA 18–25 µg/dL). Kidney damage is detectable but function is still largely preserved. Clinical signs are typically absent at this stage.
- Stage II: Creatinine 140–249 µmol/L. Mild renal azotaemia. Signs may be subtle — slight increase in thirst and urination, occasional vomiting. This is often when CKD is first diagnosed in practice.
- Stage III: Creatinine 250–439 µmol/L. Moderate renal azotaemia. More obvious signs including weight loss, poor coat condition, reduced appetite and lethargy. Quality of life may be significantly impacted.
- Stage IV: Creatinine above 440 µmol/L. Severe renal azotaemia. Uraemic crisis is a risk; hospitalisation and intensive supportive care may be required. Prognosis is guarded to poor.
SDMA is a particularly sensitive marker that can detect a reduction in kidney function before creatinine becomes elevated, making it valuable for early diagnosis. WSAVA guidelines recommend SDMA testing as part of routine annual senior wellness screening from seven years of age.
The Role of Phosphate Restriction
Phosphate accumulation is one of the most significant drivers of CKD progression in cats. Healthy kidneys efficiently excrete dietary phosphate, but as kidney function declines, phosphate builds up in the blood (hyperphosphataemia), stimulating the release of parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF-23). Chronically elevated PTH causes renal secondary hyperparathyroidism, which accelerates kidney damage and causes demineralisation of bone.
Restricting dietary phosphate intake is therefore a cornerstone of CKD management at every IRIS stage. At Stage I-II, dietary restriction alone (targeting serum phosphate below 1.45 mmol/L) is usually sufficient. At Stages III and IV, phosphate binders are frequently added alongside a restricted diet to achieve target levels.
Renal Diets
Veterinary renal diets are specifically formulated to be restricted in phosphorus and protein, while providing highly digestible, high-quality protein to minimise the production of uraemic waste products without causing muscle wasting. They also typically contain enhanced levels of omega-3 fatty acids (which reduce renal inflammation), antioxidants, and B-vitamins lost through excessive urination.
- Hills Prescription Diet k/d: One of the most extensively researched renal diets, supported by clinical studies showing a significant reduction in uraemic episodes and improved survival time in cats with CKD. Available in both dry and wet formulations, with a range of flavours to improve palatability.
- Royal Canin Renal: A palatable and widely used renal diet with a dedicated range for cats — including mousse textures well-suited to cats with reduced appetites. The range includes a urinary tract-supportive variant for cats with concurrent urolithiasis.
- Purina Pro Plan Veterinary Diets NF Kidney Function: Another phosphate-restricted, protein-moderated option, available in early-care (Stage I-II) and standard formulations, allowing dietary adaptation as the disease progresses.
Both Hills k/d and Royal Canin Renal are readily available through Zooplus, which stocks a comprehensive range of veterinary prescription diets. Subscription delivery can simplify the logistics of maintaining a consistent renal diet long-term, which is important because dietary transitions for CKD cats should be gradual to maintain food acceptance.
Phosphate Binders
When dietary restriction alone is insufficient to control serum phosphate — typically from IRIS Stage III onwards — phosphate binders are added to the treatment plan. These agents bind phosphate in the gastrointestinal tract before it is absorbed, reducing the phosphate load reaching the bloodstream.
- Pronefra: A palatable oral gel containing aluminium hydroxide and calcium carbonate as phosphate-binding agents, along with chitosan and magnesium carbonate. It is easy to administer and generally well accepted by cats.
- Epakitin: Contains chitosan and calcium carbonate. Supplied as a palatable powder that can be mixed into food. Also has some evidence for modestly reducing blood urea nitrogen and creatinine levels in addition to its phosphate-binding effect.
Hydration: Wet Food and Water Fountains
Maintaining adequate hydration is critically important in cats with CKD. Cats evolved as desert animals with a naturally low thirst drive and are prone to consuming insufficient water when fed exclusively on dry food. For cats with CKD, chronic low-level dehydration exacerbates renal stress and accelerates disease progression.
Switching to, or increasing the proportion of, wet food is one of the most impactful dietary changes an owner can make. Wet food typically contains 70–80% moisture compared with approximately 10% in dry food, substantially increasing daily fluid intake. Warming food slightly can also increase its aroma and palatability for cats with reduced appetite.
Many cats prefer running water to still water, making water fountains an effective strategy for encouraging drinking. Offering multiple water bowls in different locations around the home and keeping them scrupulously clean also helps. In some cases, subcutaneous fluid administration at home — taught to owners by their vet — becomes an important part of managing more advanced CKD.
Potassium Supplementation
Hypokalaemia (low blood potassium) is common in cats with CKD due to increased urinary potassium loss. Low potassium causes muscle weakness, ventroflexion of the neck, lethargy and poor coat condition, and can itself worsen renal function in a damaging cycle. Potassium supplementation, typically in the form of potassium gluconate (such as Tumil-K), is recommended when blood potassium falls below 3.5 mmol/L. Regular electrolyte monitoring is an important part of CKD follow-up care.
Semintra (Telmisartan) — EU-Licensed Treatment
Semintra (telmisartan) is an angiotensin II receptor blocker (ARB) licensed in the European Union specifically for the treatment of proteinuria associated with CKD in cats. Protein in the urine (proteinuria) is a significant marker of CKD severity and an independent risk factor for disease progression. By reducing proteinuria, Semintra helps to slow the rate of kidney function decline. It is administered as an oral solution once daily, making it relatively easy to give to cats. It also has a blood pressure-lowering effect, which is beneficial since hypertension is a common complication of feline CKD and can cause ocular, cardiac and neurological damage if uncontrolled.
Monitoring and Ongoing Care
Cats with CKD require regular veterinary monitoring — typically every three to six months for stable Stage II cats and more frequently for higher stages. Blood pressure measurement, urinalysis, SDMA, creatinine, electrolytes and urine protein:creatinine ratio are the key parameters to track. With attentive management, many cats with Stage II-III CKD live comfortably for two or more years after diagnosis. Speak with your vet about a tailored monitoring plan and do not hesitate to seek advice if you notice any changes in your cat's drinking, eating, or general behaviour between appointments.