Chronic kidney disease (CKD) is the most common condition of older cats — affecting approximately 30–40% of cats over 10 years of age. It is progressive and incurable but manageable, with appropriate care enabling good quality of life for months to years after diagnosis. Understanding the stages, management options, and welfare indicators is essential for cat owners and veterinary teams.
Pathophysiology
CKD involves progressive loss of functional nephrons (kidney filtering units) over months to years. Unlike acute kidney injury, CKD is characterised by structural changes — fibrosis, tubular atrophy, glomerulosclerosis — that develop gradually. Clinical signs typically emerge when 75%+ of kidney function is lost. Common underlying causes include polycystic kidney disease (hereditary in Persians), chronic interstitial nephritis, glomerulonephritis, and renal lymphoma. Many cases have no identifiable underlying cause.
IRIS Staging
The International Renal Interest Society (IRIS) staging system classifies feline CKD by serum creatinine and SDMA (symmetric dimethylarginine) levels, with substaging by proteinuria and blood pressure:
- Stage 1: SDMA 18–25 μg/dL; creatinine <140 μmol/L — minimal signs
- Stage 2: Creatinine 140–250 μmol/L — mild azotaemia; PU/PD may be present
- Stage 3: Creatinine 251–440 μmol/L — moderate; weight loss, inappetence, vomiting
- Stage 4: Creatinine >440 μmol/L — severe uraemia; profound welfare compromise
Management Strategies
Diet: Prescription renal diets provide phosphorus restriction, modified protein levels, and alkalising agents. Phosphorus restriction is the most evidence-based intervention for slowing CKD progression. Cats reluctant to eat renal diet may be managed with phosphate binders instead.
Phosphate binders: Aluminium hydroxide, lanthanum carbonate, or calcium carbonate added to food reduces intestinal phosphorus absorption — essential for cats not accepting renal diet.
Antihypertensive therapy: Amlodipine (calcium channel blocker) is first-line for hypertension — critical for preventing ocular and renal damage from systemic hypertension.
Subcutaneous fluids: Home administration of SQ fluids (Hartmann's or saline) maintains hydration in late Stage 2 and beyond, reducing uraemic signs and improving quality of life.
Potassium supplementation: Hypokalaemia is common in CKD cats and causes muscle weakness — potassium gluconate supplementation corrects this.
Welfare Monitoring
Regular monitoring (every 3–6 months in Stages 1–2, more frequently in advanced disease) tracks disease progression. Owner-reported quality of life assessment — appetite, activity, social behaviour, grooming — provides welfare status information between visits. Vomiting, profound inappetence, or sudden deterioration requires urgent veterinary assessment. End-of-life decisions are guided by quality of life assessment, not kidney values alone.