Chronic kidney disease in cats: the most common pathology of the senior cat

Chronic kidney disease affects between 28 and 38% of cats over ten years old, according to the major European and American studies (Marino et al., 2014; Polzin, 2017). Above fifteen years, prevalence exceeds 50%. It's the leading cause of natural death in senior cats and, paradoxically, one of the feline pathologies with the best intervention margin if diagnosed early. The difference between detecting it at IRIS stage 1 and detecting it at IRIS stage 4 is years of life.

What happens when a feline kidney becomes diseased

The kidney filters about 150 liters of plasma per day in an adult cat. The functional unit, the nephron, does not regenerate. When a nephron is lost, the remaining ones hypertrophy to compensate. There comes a point where functional reserve is exhausted and visible consequences appear: loss of urine-concentrating capacity, accumulation of nitrogenous products, hyperphosphatemia, anemia from erythropoietin deficit, hypertension, metabolic acidosis.

Feline CKD is, in 80% of cases, idiopathic (no single identifiable cause). The combination of genetic factors, diet, chronically deficient hydration, and chronic inflammatory processes is suspected to contribute to deterioration over years. There is a 20% with identifiable causes:

• Glomerulonephritis secondary to infectious or immune-mediated processes.
• Chronic pyelonephritis from poorly resolved ascending urinary infections.
• Renal amyloidosis, especially in Abyssinian, Siamese, and Oriental breeds.
• Polycystic kidney disease (PKD) in Persian, Exotic, and related breeds.
• Chronic urethral obstructions with retrograde damage.
• Toxicity (ethylene glycol antifreeze, lilies, inappropriate NSAIDs).

Clinical signs worth identifying early

The cat compensates very well for loss of renal function. When visible signs appear, it has already lost approximately 65-75% of functional nephrons. Early signs:

• Polydipsia (drinking more water). A healthy cat drinks 50-80 ml per kg of body weight per day. A cat with stage 2 CKD can triple intake.
• Polyuria (urinating more). The litter box gets soaked sooner and more often.
• Slow weight loss (2-4 lb over several months).
• Dull coat.
• Progressive appetite decline or "food fussiness" (yesterday it ate chicken, today it doesn't).

Advanced signs (stage 3-4):

• Uremic halitosis (ammonia-like breath).
• Frequent vomiting.
• Sustained anorexia.
• Oral ulcers.
• Marked lethargy.
• Hypertension with visual signs (acute retinal detachment, sudden blindness).
• Anemia with pale mucous membranes.

The ISFM/AAFP consensus (Sparkes et al., 2016) recommends annual bloodwork from age seven and biannual from age twelve, even in apparently healthy cats.

The IRIS staging system

The International Renal Interest Society has published the worldwide reference staging system since 2006. Last revised in 2023, it combines four parameters: serum creatinine, SDMA (symmetric dimethylarginine, an early marker), proteinuria (UPC, urine protein-creatinine ratio), and systolic blood pressure.

Main stages

Stage	Creatinine (mg/dL)	SDMA (µg/dL)	Clinical significance
1	<1.6	14-18	Renal damage without clear azotemia
2	1.6 to 2.8	18-25	Mild azotemia, first intervention
3	2.9 to 5.0	26-38	Moderate azotemia, clinical signs
4	>5.0	>38	Severe azotemia, uremic crisis risk

Sub-staging

Two sub-stages overlay the main stage:

• Proteinuria (UPC): non-proteinuric (<0.2), borderline (0.2-0.4), proteinuric (>0.4). Persistent proteinuria accelerates deterioration.
• Blood pressure: normotensive (<140 mmHg systolic), prehypertensive (140-159), hypertensive (160-179), severely hypertensive (≥180).

A cat at IRIS 2, non-proteinuric, normotensive, has a prognosis of years. A cat at IRIS 2, proteinuric, hypertensive, has a prognosis of months unless intervened on all three fronts.

Diagnosis

A complete renal evaluation panel in a cat includes:

1. Serum creatinine and BUN.
2. Serum SDMA (around $30-50 extra in the U.S.; provides detection 12-18 months before creatinine).
3. Serum phosphorus and calcium.
4. Potassium.
5. Urine specific gravity (urine collected at home or via cystocentesis).
6. UPC (proteinuria).
7. Urinary sediment (rule out infection).
8. Systolic blood pressure measured in a calm exam room.
9. CBC (rule out regenerative or non-regenerative anemia).
10. Abdominal ultrasound (rule out cysts, masses, obstruction).

Total cost at a U.S. private veterinary clinic in 2026 runs around $400-700. In senior cats, taking this on annually is reasonable.

Treatment by stage

IRIS 1: monitoring and prevention

• Increase hydration: active fountain, wet food as the base.
• Reduce stressors that can trigger deterioration (conflictual multi-cat households, marking, anxiety).
• Repeat bloodwork every 6 months.

IRIS 2: first real intervention

• Prescription renal diet. Improves documented survival by 24-36 months of median.
• RAAS inhibitor (telmisartan or benazepril) if proteinuria is present.
• Antihypertensive (amlodipine) if hypertension is present.
• Sustained intensive hydration.

IRIS 3: multimodal treatment

• All the above, plus:
• Phosphate binders (aluminum hydroxide, lanthanum, sevelamer) if phosphorus doesn't drop with diet alone.
• Oral potassium supplementation if hypokalemia.
• Antiemetics (maropitant, ondansetron) for vomiting.
• Appetite stimulants (mirtazapine, capromorelin).
• At-home subcutaneous fluid therapy two to three times a week.
• Oral bicarbonate if sustained acidosis.

IRIS 4: crisis management

• Hospitalization for IV fluid therapy during uremic crises.
• Erythropoietin (darbepoetin) if severe anemia.
• Consider peritoneal dialysis in selected cases, available at U.S. veterinary teaching hospitals.
• Humane euthanasia when quality of life degrades irreversibly.

Real prognosis

Real data from European and American studies (Boyd 2008, Marino 2014, Polzin 2017):

• IRIS 1: the cat may never die from CKD. Annual monitoring.
• IRIS 2: median survival of 24 to 36 months with renal diet and appropriate treatment. Without treatment, median 12-18 months.
• IRIS 3: median 10 to 18 months with treatment. Without treatment, 3-6 months.
• IRIS 4: median under 6 months even with intensive treatment.

The most powerful prognostic predictor is no longer the baseline stage: what informs most is the rate of progression between two bloodwork panels six months apart. A cat with stable creatinine between two checks can live for years. A cat with creatinine rising 0.5 mg/dL per quarter has a prognosis of months.

Hydration, the underestimated lever

A cat with CKD loses the ability to concentrate urine. To clear the same nitrogenous products as a healthy kidney, it needs more water volume. If water intake doesn't compensate, the cat becomes chronically dehydrated and the kidneys feel it within days.

Three concrete home measures:

1. Active fountain instead of a static bowl. Increases intake by 1.5-2x.
2. Wet food predominance in the diet. A can provides 75-80% water; dry kibble less than 10%. In CKD, 70/30 in favor of wet is reasonable.
3. Multiple drinking points spread around the house. Cats drink more when fountains are accessible.

In IRIS 3-4, at-home subcutaneous fluid therapy is the most effective tool. The vet teaches the owner to administer saline (lactated Ringer's, 0.9% NaCl) subcutaneously two or three times a week at home. It's a simple intervention with a one-week learning curve.

Breeds with elevated prevalence

• Persian, Exotic, and British Shorthair: linked to genetic PKD (PKD1 mutation).
• Abyssinian, Siamese, and Oriental: renal amyloidosis with genetic basis.
• Maine Coon: elevated prevalence of senile CKD.
• Ragdoll: linked to secondary HCM-related disease.

In predisposed breeds, the PKD genetic test (Persian, Exotic) and annual bloodwork from age six are reasonable screening measures.

What can NOT be done

• Reverse the damage. Lost nephrons don't regenerate. Treatment slows, it doesn't cure.
• Kidney transplant in many regions. The option exists at some U.S. veterinary teaching hospitals (UC Davis, University of Wisconsin, Penn Vet) but is not available at most private clinics.
• Massive supplementation with vitamins and minerals without prescription. Excess phosphorus or calcium in a cat with CKD accelerates deterioration.

Conclusion

CKD is the most common pathology of the senior cat and, paradoxically, one of those most responsive to early intervention. Detection at stage 1-2 through annual bloodwork with SDMA is the difference between years and months of prognosis. The renal diet remains, two decades after foundational studies, the lever with the most evidence for extending survival. Combined with intensive hydration, phosphorus control, and management of hypertension and proteinuria, it gives most cats diagnosed at IRIS 2 two to three years of quality life.

Sources

• International Renal Interest Society (IRIS). Staging of CKD in cats, 2023 revision. iris-kidney.com
• Sparkes, A. H. et al. (2016). ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. JFMS 18, 219-239.
• Polzin, D. J. (2017). Chronic kidney disease in small animals. Veterinary Clinics of North America 41, 15-30.
• Marino, C. L. et al. (2014). Prevalence and classification of chronic kidney disease in cats. JFMS 16, 465-472.
• Boyd, L. M. et al. (2008). Survival in cats with naturally occurring chronic kidney disease. JVIM 22, 1111-1117.