Kidney Disease (CKD)

By Aimee Castor, DVM

City Cat Mobile Vet Service

Kidney failure, also called chronic kidney disease (CKD), is a very common illness in older cats.  The exact cause is unknown but it is believed that high blood pressure, hereditary factors, and even dental disease may contribute to kidney disease. 

The kidneys are responsible for many important things: 

1.  They filter toxins from the blood.

2.  They reabsorb fluid, preventing the body from becoming dehydrated.

3.  They help to eliminate phosphorous, keeping the level in the blood within normal limits.

4.  They stimulate the bone marrow to make red blood cells.

When the kidneys become compromised, toxic products can no longer be processed effectively and the toxins accumulate in the blood. In effect, a cat with CKD is being poisoned by the toxins that the kidneys are unable to remove. Dehydration, electrolyte imbalances, anemia, and blood pressure problems may also occur as the kidneys continue to deteriorate.  

The first things that are noticed with kidney disease are increased drinking and an increased volume of urine.  As the loss of kidney function continues, the cat may become lethargic, lose its appetite, and lose weight.  At this point, less than 25% of the kidney tissue is working.  The toxins (BUN and creatinine) are building up in the blood and poisoning the system.  This is called uremia.  The phosphorous in the bloodstream may increase at this time, as well.  In advanced cases, anemia can occur because the kidneys no longer stimulate the bone marrow to make new red blood cells.  

CKD is irreversible and progressive in nature but clinical signs can be alleviated and the progression can be slowed via treatment.

Stages of kidney disease:

Grade 1 creatinine <1.6

Grade 2 creatinine 1.6 to 2.9 (Increased drinking and urination)

Grade 3 creatinine 2.9 to 5.0 (Systemic signs such as bone pain, gastritis, and anemia)

Grade 4 creatinine >5.0 (Increased severity of systemic signs and uremic crisis)

Other complications of kidney disease:


By far the most important treatment is correction of dehydration, which occurs commonly in cats with stage 3 and 4 kidney disease.  Most chronic renal failure patients have polyuria which means they produce excessive amounts of urine due to loss of kidney function.  In addition, vomiting and/or diarrhea can be present, both of which contribute to water loss and dehydration.  Without correction of the resulting dehydration, fluid deficits will lead to a rapid and severe decline of renal function.    If your cat is severely dehydrated, we will advise that he or she be hospitalized for the administration of intravenous fluids.  Intravenous (IV) fluids are sterile fluids that contain electrolytes and are injected directly into a vein.  Compared with other routes of administration, the intravenous route is the fastest way to deliver fluids and the most beneficial to cats that are severely dehydrated.  A sterile catheter (a flexible plastic tube) that contains a needle is pierced through the skin and into a vein, usually on a front leg.  The needle is then removed and discarded, while the soft catheter stays in the vein. The external portion of the catheter, which is taped in place, is then hooked up to an IV line and bag of  IV fluids.  The IV fluids are started at a slow but constant rate, while the cat is closely monitored.  In serious cases this is the only chance we have to save your cat’s life.  If the cat is going to improve, it usually does so within 24 to 48 hours, at which point it can be started on subcutaneous fluid therapy.


Subcutaneous fluid therapy consists of injecting fluids under the skin.  These fluids are slowly absorbed by the animal and correct dehydration.  It lowers the concentration of BUN and creatinine in the bloodstream and corrects electrolyte disorders, allowing your cat to feel better.  Often cats improve greatly due to subcutaneous fluids and we can teach you to administer the fluids so that you can give them at home.  Sometimes cats need to be on subcutaneous fluids (usually given 2 to 3 times a week) for the rest of their life and other times they can be taken off the subcutaneous fluids and maintained on a kidney diet (see below).


Some cats with renal disease have hypokalemia, or low potassium, which causes muscle weakness and pain, and can be detected with blood work. This condition must be corrected because it can be life threatening.  Potassium may be added to IV or subcutaneous fluids to treat hypokalemia or it can be given orally in mild cases.


Elevated phosphorus is common with kidney issues. It is important to normalize phosphorus because if it stays elevated, it can cause further damage to the kidneys.  Subcutaneous or IV fluids will lower phosphorus levels. However, if phosphorus is still high after the cat is rehydrated, aluminum hydroxide should be used to further lower the phosphorus.  The daily dosage of aluminum hydroxide must be divided and given with each meal to be effective.  It may be obtained over the counter in liquid form such as Mylanta, but many cats do not like the taste of the over-the-counter liquid form. Instead, we recommend a powdered form that can be mixed in canned food and may be obtained at:

Be careful not to overdose your cat with aluminum hydroxide because too much can also cause problems.

High blood pressure

In one study, 61percent of cats with kidney disease had high blood pressure.  High blood pressure can detach the retina of the eye causing blindness, further damage the kidneys, and increase the risk of a blood clots. Taking the blood pressure in cats is more difficult than humans.  An ultrasonic probe must be held over the artery and then, using ultrasound, the sound of the systolic pressure is converted into an audible signal.  The most accurate instrument for taking blood pressure in cats is the Park’s doppler shown to the right.  High blood pressure is treated with amlodipine which comes in pills or can be compounded into liquid by a compounding pharmacy.


Anemia often occurs in cats with moderate to severe kidney disease because the kidney is partially responsible for manufacturing red blood cells.  Epogen, a form of erythropoetin that the kidneys use to manufacture red blood cells, can be given to treat this type of anemia.  However, the downside to treating the cat with Epogen is that antibodies can form causing the cat’s immune system to destroy the red blood cells.  For this reason, Epogen should be used only when the anemia is severe.


Cats with renal failure are predisposed to kidney infections called pyelonephritis.  Pyelonephritis causes the symptoms to become much worse and can cause further damage to the kidneys.  For this reason, routine urinalyses and urine cultures are important to detect infections.  We culture the urine in house using a thioglycolate culture medium also referred to as “thiobroth” because it is much more sensitive than the traditional methods used to culture the urine at commercial laboratories.  If the culture is positive, it is sent out to a laboratory for a test that determines which antibiotic the bacteria is sensitive to so that appropriate treatment can be selected. 


A diet that supports the kidneys is also an important treatment.  Prescription kidney diets are controversial because they contain low protein.  BUN and Creatinine, the toxins that the kidneys are responsible for removing from the bloodstream, are manufactured from protein, and therefore the restriction of protein, in theory, decreases the amount of BUN and Creatinine in the blood.  However, this theory has never been proven in cats.

Kidney diets also restrict phosphorus which has been shown to slow the progression of kidney disease.  

Other important ingredients of kidney diets include omega 3 fatty acids which decrease inflammation,  and ingredients that alkalinize the urine and blood, minimizing acidosis.  Acidosis is common in renal failure and causes a loss of appetite, nausea, vomiting, weight loss, lethargy, weakness and muscle wasting.

The most important thing regarding diets in cats with renal failure is that they like the diet and eat it.  Many cats will not eat prescription kidney diets and therefore choosing a diet that is low in phosphorus and supplementing it with omega 3 fatty acids may be the best thing to do.

The following is a list of the phosphorus content of various diets:

For an Omega-3 fatty acid source see alternative medicines later in this article.

Other Medications:


When kidney disease progresses in cats, the calcium and phosphorus levels become abnormal causing the bones to become soft and bendable, leading to bone and joint pain.  Small doses of Calcitriol (vitamin D) help the situation.  It is given twice weekly and comes in either liquid or capsule form.  At this time no formal tests have been run on cats to determine if Calcitriol improves kidney function, but it has shown to decrease the progression of kidney disease in dogs.  In addition, veterinarians surveyed believe that it has improved the comfort of their feline patients.  Calcitriol can be started in early kidney disease to decrease its progression.  We generally have Calcitriol compounded into liquid or pills and given twice weekly and we recommend that the calcium and phosphorus levels are checked one month after starting treatment, and then every six months.

Alternative medications:

Renal Essentials by Vetriscience contains rehmannia, nettle seed, cordyceps, astragalus, arginine, and omega-3 fatty acids.  This is an alternative medicine that was designed to improve renal function.  It comes in big tablets that have a pleasing flavor.  Some cats will eat the tablets but many will not, so crushing them up with a pill crusher and mixing them into canned food or breaking them into pieces and putting them into pill pockets may be necessary to get them to take the medication.