Chronic kidney disease (CKD) is the most common pathology in cats over 7 years old and the second leading cause of death in domestic cats, second only to tumors. It is estimated that 30-40% of cats over 12 years of age suffer from it to some degree. Although there is no cure, early diagnosis and proper management can significantly slow its progression and preserve quality of life for years.
Why Cats Are So Susceptible to Kidney Damage
Feline kidneys have limited regenerative capacity. Once nephrons (the functional units of the kidney) are lost, they cannot be recovered. Cats are also obligate carnivores with a metabolism that generates large amounts of nitrogenous waste products that must be filtered by the kidneys. Combined with their tendency to chronic dehydration (they drink little naturally), the feline kidney constantly works at its limit.
The most frequent causes of CKD in cats include: chronic tubulointerstitial nephritis (most common cause, multifactorial origin), glomerulonephritis, recurrent bacterial pyelonephritis, polycystic kidney disease (hereditary in Persians and related breeds), renal neoplasms and damage from chronic hypoperfusion.
The Late Diagnosis Trap
One of the main problems with feline CKD is that clinical signs appear when more than 75% of kidney function has already been lost. Cats, like most felines, are experts at hiding discomfort. That is why annual blood and urine tests from age 7 are essential, not optional.
Serum creatinine, the classic kidney marker, only rises when kidney function has fallen below 25%. The biomarker SDMA (symmetric dimethylarginine) detects CKD with a 40% functional loss, i.e., much earlier. Since 2015 it has been available in reference veterinary biochemical profiles and has transformed the early diagnosis of feline CKD.
IRIS Classification and Staging
The International Renal Interest Society (IRIS) classifies feline CKD into four stages based on serum creatinine and SDMA, with sub-staging based on blood pressure and proteinuria:
- Stage 1: elevated SDMA, normal creatinine (<1.6 mg/dL). No clinical signs. Diagnosis is only possible with SDMA.
- Stage 2: creatinine 1.6-2.8 mg/dL. Mild polyuria/polydipsia. Most cats are at this stage at diagnosis.
- Stage 3: creatinine 2.9-5.0 mg/dL. Evident clinical signs: weight loss, vomiting, poor coat condition, anorexia.
- Stage 4: creatinine >5.0 mg/dL. Uremic crisis. Reserved prognosis.
Management and Treatment
The goal of treatment is not to cure CKD (impossible), but to slow its progression and control clinical signs:
Renal diet: foods specifically formulated for CKD (Hill's k/d, Royal Canin Renal, Purina NF) have moderate restriction of phosphorus, sodium and protein, with high digestibility. They are the cornerstone of treatment in stages 2-4. Phosphorus restriction is especially critical: secondary renal hyperparathyroidism caused by hyperphosphatemia is one of the main mechanisms of progressive kidney damage.
Hydration: since cats with CKD produce large volumes of dilute urine, maintaining adequate hydration is essential. Wet or semi-moist feeding is recommended, along with running water sources, and in advanced cases, subcutaneous fluid therapy at home (administered by the owner after veterinary training).
Blood pressure control: 60-70% of cats with CKD develop hypertension. Amlodipine is the first-line antihypertensive in cats.
Proteinuria control: if the urinary protein/creatinine ratio (UPC) is >0.4, treatment with benazepril or telmisartan (ACE inhibitor/ARB) is started to protect the glomerulus.
Anemia management: non-regenerative anemia is common in advanced stages due to erythropoietin deficiency. Darbepoetin alfa (EPO analog) may be necessary in cats with hematocrit <20%.
Follow-up: Consistency Makes the Difference
Cats with CKD stage 2 should be checked every 3-6 months; those at stage 3-4, every 1-3 months. Each visit should include complete blood work, urinalysis, blood pressure and body condition assessment. Owners committed to follow-up can keep their cats in good quality of life for years, even with advanced CKD.
