What it is
The kidneys filter waste products from the blood, regulate fluid balance, produce hormones involved in blood pressure control and red blood cell production, and maintain electrolyte balance. In CKD, nephrons — the functional units of the kidney — are progressively lost and cannot regenerate. As nephron mass declines, the remaining nephrons compensate by hyperfiltrating, which itself accelerates their eventual loss.
Cats are particularly susceptible to CKD. The exact reasons are not fully understood, but factors include the obligate carnivore diet (which places a high metabolic load on the kidneys), lifelong moderate dehydration (cats evolved in arid environments and have a blunted thirst drive), and the high prevalence of conditions that secondarily damage the kidneys — hyperthyroidism, hypertension, dental disease bacteraemia, and chronic low-grade inflammation.
The IRIS staging system
The International Renal Interest Society (IRIS) provides the internationally accepted framework for staging and managing feline CKD. Staging is based on fasting creatinine and SDMA values, with substaging by blood pressure and urine protein loss:
No clinical signs. Detected only by blood and/or urine testing. Intervention at this stage (diet, blood pressure monitoring) has the greatest potential impact on slowing progression. Requires SDMA testing — creatinine is not yet elevated.
Clinical signs minimal or absent. Increased thirst and urination may be noted. Renal diet transition recommended. Most responsive to dietary management. Median survival years with appropriate management.
Weight loss, reduced appetite, nausea, and lethargy typically apparent. Anti-nausea medication, appetite stimulants, and phosphate binders commonly added. Subcutaneous fluid therapy often introduced. Regular monitoring every 1–3 months.
Uraemic crisis signs possible: vomiting, mouth ulcers, severe weight loss, profound lethargy. Management focuses on comfort and quality of life. Prognosis guarded — median survival months. Quality of life assessment becomes the central consideration.
Early detection
The kidneys can lose approximately 75% of function before creatinine rises on standard blood tests. SDMA — a newer biomarker — elevates when only about 25% of function is lost, enabling diagnosis up to two years earlier than creatinine-based testing. Read our news article on feline CKD prevalence and SDMA adoption for the UK data.
From age 7, request that SDMA is included in annual blood panels. Not all practices include it as standard — it is worth specifically asking. Our routine check-up guide explains what is typically included in senior blood panels and how to ensure comprehensive testing.
Management overview
- Prescription renal diet: reduced phosphorus, controlled protein — the single most evidence-based intervention for slowing progression
- Hydration: wet food, water fountains, and subcutaneous fluids in moderate-advanced disease — see our cat hydration guide
- Phosphate binders: oral aluminium hydroxide or lanthanum carbonate given with meals to reduce dietary phosphate absorption
- Blood pressure management: amlodipine for systemic hypertension, which is common in CKD cats
- Anaemia management: erythropoiesis-stimulating agents in Stage 3–4 cats with symptomatic anaemia