A vet checks a Ragdoll cat's heart rate.

Chronic Kidney Disease in Cats

Kidney (renal) disease is extremely common in aging cats. It can be acute onset, but is typically seen as a chronic age-related change diagnosed later in the course of the disease.

Understanding kidney disease involves having an understanding of the anatomy and function of the kidneys. The kidneys filter blood from the circulating blood stream and remove waste to create urine. They are also responsible for helping to maintain a healthy water balance and work to regulate sodium, potassium, calcium, and phosphorus levels.

Kidneys also help to maintain a normal blood pressure and produce hormones to promote red blood cell formation. Without normal renal function, all of these essential processes can fail. The kidneys are made up of millions of nephrons, which contain a glomerulus responsible for filtering and the tubule, which helps transport waste and filter blood to the appropriate locations. The loss of functioning nephrons causes the remaining nephrons to work harder, which ultimately causes damage. One theory for the development of renal disease in cats is thought to be secondary to chronic interstitial nephritis (CIN), which is identified by advanced fibrosis, loss of nephrons, and sterile inflammation, leading to tubulointerstitial disease.

Symptoms of Kidney Disease

Clinical signs of chronic renal disease in cats tend to be subtle and progressive.

The most common signs are:

Cats that exhibit symptoms should be evaluated by a veterinarian. There are other diseases in older cats that can mimic renal failure and should be addressed and determined as the underlying cause. Diseases that can mimic renal failure with similar clinical signs include:

If a cat is suspected to have underlying kidney disease, your veterinarian will perform a full physical exam. On exams, they assess hydration, palpate the kidneys, and look for muscle loss, any evidence of a heart murmur, and pale mucous membranes. Cats with chronic kidney disease will often be dehydrated, because the kidneys are not functioning appropriately and, therefore, are causing excess water to be lost in the urine. Because the kidneys are responsible for making a hormone called erythropoietin that assists in the creation of red blood cells, cats with kidney disease often have pale mucous membranes and suffer from anemia. Cats with underlying anemia can have a heart murmur and should be auscultated when performing a physical exam. Palpation may also present small, misshapen kidneys. If a cat has pain or oversized kidneys, they need to be assessed for renal cancer or a kidney infection (pyelonephritis).

Evaluation and Testing for Kidney Disease in Cats

Ultimately, kidney function is evaluated by performing further diagnostics, including:

Kidney Disease Staging and Substaging

Chronic kidney disease has been categorized by The International Renal Interest Society (IRIS). This society has helped to create a standardized staging system for cats and dogs with renal disease. Having an accepted staging system creates a coherent and easy-to-follow method all veterinarians can use that avoids subjective variance. The staging system is primarily based on blood creatinine levels, with a subset of staging based on urine protein creatinine ratio and blood pressure.

IRIS staging of CKD in cats:

Stage Blood Creatinine (umol/l & mg/dL) SDMA (ug/dL)
1 <140, <1.6 <18
2 140 – 250, 1.6 – 2.8 18 – 25
3 251 – 440, 2.9 – 5.0 26 – 38
4 >440, >5.0 >38

Proteinuria substaging in cats:

UP/C value Substage
<0.2 Non-proteinuric
0.2 – 0.4 Borderline proteinuric
>0.4 Proteinuric

Blood pressure substaging in cats:

Systolic Blood Pressure Blood Pressure Substage Risk of Future Target Organ Damage
<140 mmHg Normotensive Minimal
140 – 159 mmHg Prehypertensive Low
160 – 179 mmHg Hypertensive Moderate
>180 Severely hypertensive High

All cats should be reevaluated after treatment has been initiated, then serially at recheck appointments to monitor improvement or worsening.

Treatment of Renal Disease

Treatment of chronic renal failure is multifactorial and highly dependent on each patient.

A few keys to treatment include:

Ultimately, working with your veterinarian to create the best treatment plan for your cat is recommended. Frequent monitoring of renal values, electrolytes, and blood pressure are needed to monitor progression of disease and success of treatment.