Kidney Disease in Cats—By Dr. Kimberly Couch

The kidneys have many vital functions. They primarily act by filtering waste from the bloodstream, regulating the number of essential minerals (potassium, phosphorus, and sodium) present in the bloodstream, conserve water, and produce urine. Many cats develop deficiencies in their kidneys as they age. A diagnosis of kidney disease can be very confusing and overwhelming to cat owners. In this article I will discuss what exactly kidney disease is and how it can be managed by cat owners and their veterinarians.

Types of Kidney Disease

In general, the kidneys can function normally until ⅔ of the kidneys are damaged. Once this degree of damage has occurred, clinical signs of kidney disease are seen, and kidney function is compromised. There are two types of kidney disease- acute kidney injury and chronic kidney disease.

Acute kidney injury (AKI) is a more severe issue that presents with very abrupt clinical signs when compared to the more gradual clinical signs of chronic kidney disease.

AKI is usually secondary to things like kidney stones, kidney infections, kidney cancer, or toxicities (raisins, lilies, leptospirosis, etc.). Chronic kidney disease (CKD) is very common in older cats, and the signs take months to years to develop and be clinically obvious. Additionally, there are different parts of the kidneys that have different functions.

The glomerulus of the kidney is responsible for deciding which proteins are kept in the bloodstream and which ones can be excreted in the urine.

The renal tubules are responsible for producing urine and controlling what minerals stay in the blood and what is excreted. Depending on the degree of damage, one or both parts can be affected. Similarly, if chronic kidney disease progresses far enough, it can cause a secondary acute kidney injury.

Stages of CKD 

The degree of damage to the kidneys is graded using a numerical scale from 1-4, with substages based on lab work values and blood pressure. The stage of kidney disease, along with clinical signs, determines the treatment recommendations. 

Diagnosis

Early kidney disease can be diagnosed based on annual wellness bloodwork. Kidney enzymes (BUN, Creatinine, and SDMA) are typically elevated with a low urine specific gravity. In more severe cases, blood phosphorus levels may be elevated, and blood sodium levels may be low.

Additionally, in advanced cases, blood protein may be low, and protein may be present in the urine. Red blood cell count may also be low. Patients with CKD may also have urinary tract infections.

Depending on the severity of the results, sometimes your veterinarian will recommend just to monitor these values over time or recheck them in a few weeks to show progression. Other times, treatment and additional diagnostics may be recommended. 

Clinical Signs

Early signs of chronic kidney disease include poor coat quality and decreased grooming activity or weight loss. Owners may also notice increased amounts of urine and consequently an increased water intake. In cases of more advanced kidney disease, cats may appear lethargic or sick (vomiting, diarrhea, inappetence).

It is important to understand that there is not a cure for chronic kidney disease. By nature, it is a chronic progressive disease, and treatment is typically aimed at controlling symptoms and slowing progression. 

●    Diet: Changing the diet is one of the easiest and most effective ways of helping to slow the progression of kidney disease. The mainstays of a diet formulated for kidney disease are that they are low in protein and phosphorous. This helps to lower the amount of waste products going into the bloodstream since the kidneys can no longer filter things out into the urine appropriately. There are many veterinary formulated diets in different flavors for this purpose. 

●    Fluids: In kidney disease, the kidneys aren’t able to excrete the normal amount of waste products they normally do due to their compromised concentrating abilities, so they compensate by producing a larger amount of dilute urine. This causes an overall reduction in body water (dehydration), and cats often need fluid supplementation to compensate. The amount of fluids can be increased in multiple ways:

○ Water fountains

○ Wet food

○ Subcutaneous fluid injections 

●    Phosphate binders: In some cats, reducing the amount of phosphorus in the diet isn’t enough. In these cases, a phosphate binding supplement can be added to the diet to reduce the amount of phosphorus entering the bloodstream.

●    Potassium supplementation: In some cats, they lose too much potassium in the urine, so it needs to be added to the diet. Low potassium can cause neurologic signs and weakness. 

●    Vitamins: Oftentimes, in cats with kidney disease, water-soluble vitamins such as B and C are lost in the urine and need to be supplemented into the diet. 

●    Anti-nausea medication: In advanced cases of CKD, the toxins can make cats feel nauseous and not want to eat. Anti-nausea medications help to reduce this feeling and encourage appetite. 

●    Blood pressure medications: Some cats with CKD have elevated blood pressure, which can worsen the progression of the disease. In these cases, blood pressure medications such as amlodipine are recommended. 

●    Anemia treatment: The kidneys are vital in the production of red blood cells. In advanced cases, this ability is reduced. Cats may need injections to help stimulate the kidneys or may even need blood transfusions.

Prevention

There are many potential causes of kidney disease in cats, such as genetic abnormalities, infections, cancer, urinary stones, etc. Sometimes cats just develop kidney disease, and the initial cause is unknown. In many older cats, the cause isn’t found, and it is attributed to a “normal” disease in older cats.

There is some supporting evidence to suggest that adequate hydration can help support renal health and may be useful in preventing diseases of the urinary system (including the kidneys).

👉 See article on The Importance of Hydration in Cats

Additionally, regular visits with your veterinarian and annual blood work may help identify the early stages of kidney disease, and early interventions can be made to slow progression. 

FAQ:

What if my cat doesn’t like the kidney diet?

There are a lot of flavors and different brands of kidney diets now. I recommend trying a few different ones and offering your cat a rotating variety. 

Balanced home-cooked diets are also a good alternative. If all else fails, it is better for your cat to eat a non-kidney diet than to refuse the kidney diet and not eat anything at all.

Is hemodialysis an option for cats like it is for people?

Hemodialysis DOES exist for cats. It is usually only available at specialty veterinary referral centers or veterinary school hospitals. While it is an option, it is most effective in cases of acute kidney injury rather than chronic kidney disease. It is also very expensive and oftentimes cost-prohibitive.

What breeds of cats are predisposed to kidney disease?

Any cat breed can develop chronic kidney disease. Some cats are predisposed to acute or chronic kidney disease due to a congenital condition called polycystic kidney disease. This condition is common in Persians, Himalayans, and exotic shorthair breeds. 

How long will my cat live once diagnosed with CKD?

This is extremely variable. This is largely dependent upon which stage your cat is first diagnosed in, how he/she responds to treatment, and how fast he/she progresses. Once diagnosed and treatment is initiated, your veterinarian will recommend rechecking lab work and diagnostics to monitor progress. Monitoring these values will help get a better idea of your cat’s individual prognosis.

Conclusion:

Many old cats are diagnosed with chronic kidney disease. While CKD is a progressive disease, symptoms can be managed, and cats can have a fairly normal life after diagnosis.

The diagnosis can be very overwhelming. However, by making some minor changes at home, you can make a huge difference for your CKD cat.