Kidney disease is is a common and life-threatening disorder which occurs when the kidneys lose their ability to filter blood as efficiently as they should, due to the loss of tiny filtering units known as nephrons. This causes metabolic wastes to build up in the blood.
Cats have two bean-shaped kidneys. They are remarkable at adapting to decreasing numbers of nephrons and it is only when approximately 75% of kidney function has been lost that kidney disease becomes apparent. The term ‘silent disease‘ is often used to describe this disease for good reason. Cats who have chronic kidney disease have had it for months or years before symptoms became apparent.
Kidney disease may be acute or chronic. Acute, which is sudden onset and can develop in cats of any age, or more commonly, chronic kidney disease, which is seen most often in cats over 10 years of age. It is the second biggest killer of cats.
Cats of any age can develop kidney disease, however, it is much more likely to develop as cats reach their senior years, with up to 50% of cats suffering from chronic kidney disease by the time they reach 15. One study suggests Burmese, Maine Coons, Persians, Himalayans, Russian Blues and British Shorthairs are more prone to developing chronic kidney disease.
Other important functions of the kidneys:
As has already been covered, the kidneys remove metabolic waste products and excess water from the bloodstream which is then passed out of the body via the urine. They also have several other important functions including:
Kidneys help control blood pressure by releasing an enzyme called renin. When blood pressure drops and kidneys don’t receive enough blood, renin is released, causing blood vessels to contract (tighten). When blood vessels contract, blood pressure goes up.
The kidneys produce a hormone known as erythropoietin, which instructs the bone marrow to produce red blood cells.
Blood acid-base regulation.
They help maintain the proper balance of acid and minerals, including sodium, calcium, potassium, and magnesium, in the blood.
What causes kidney disease in cats?
There are many causes of kidney disease in cats. Because the kidneys filter the blood, other diseases and infections can damage the kidneys. You will notice that some causes are seen in both acute and chronic kidney disease.
Acute Kidney Failure/Injury (Acute Renal Failure or ARF):
Acute kidney failure is brought about by a sudden decline in kidney function and is usually caused by a sudden injury. The two most common causes of acute renal failure are poisoning or a blockage.
There are many common household poisons which can result in damage to the cat’s kidneys. Common ones include antifreeze, lily, snake bite, pesticides, ingestion of human medications, especially NSAID’s such as Ibuprofen (Nurofen/Advil)
Previously referred to as ‘kidney failure‘ (which it isn’t until the end stage), this type of kidney disease is slow and progressive and is seen most often in senior cats. Veterinarians still aren’t entirely sure of the causes of chronic kidney disease but predisposing factors chronic kidney disease may include:
Bacterial infections and viral infections such as Feline Leukemia and FIV.
Hypertension (high blood pressure). High blood pressure can be caused by kidney disease but kidney disease can also cause high blood pressure. Either way, high blood pressure is a serious disease which can lead to blindness, seizures, stroke and coma.
High or low potassium can develop due to chronic renal disease. Potassium is an electrolyte
Periodontal (gum) disease.
Urinary tract disease.
Polycystic kidney disease.
Congenital disorders such as polycystic kidney disease, renal dysplasia.
Cancer of the kidneys.
Genetics, some family lines or breeds appear to be more predisposed to the development of chronic kidney disease.
Wear and tear. As cats age, organ function declines, some organs are able to replace lost or damaged cells (such as the liver), however, the kidney is not able to make new nephrons.
In many cases, a cause can’t be determined.
What are the symptoms of kidney disease in cats?
Polyuria (excessive urination) and polydipsia (excessive thirst) are hallmarks of kidney disease. It is always important to see your veterinarian if you notice your cat drinking and/or urinating more than usual. This occurs because the kidneys lose their ability to concentrate urine, meaning excess water is lost. To compensate, the cat drinks more but dehydration becomes a common problem among cats with kidney disease.
As metabolic waste products build up in the blood, your cat begins to feel pretty unwell. As you would well know, when you feel unwell, you lose your appetite. It is very common for cats with kidney disease to go off their food.
Other common symptoms of kidney disease include:
Hunched over appearance
As chronic kidney disease progresses, your cat may lose his appetite, stop drinking and become dehydrated even more. His breath may have an ammonia smell to it. I lost a cat to kidney disease in 2009 and in his final two days, he would sit hunched over his water bowl but not drinking. At this point, he had developed severe uremic poisoning.
What are the medical consequences of kidney disease in cats?
The impact of kidney disease affects many body systems.
Uremic poisoning – As toxins build up in the cat’s body, uremia can develop, which is life threatening as your cat is effectively being poisoned by a build-up of waste products in the body which should ordinarily be filtered out. Symptoms of uremic poisoning include:
Loss of coordination
High blood pressure – This can be caused by kidney disease but kidney disease can also cause high blood pressure. Either way, high blood pressure is a serious disease which can lead to retinal detachment and blindness, seizures, stroke and coma. Symptoms of high blood pressure are often lacking. If your cat has kidney disease or hyperthyroidism, he should have his blood pressure monitored regularly.
Electrolyte imbalances – High phosphorous, hypocalcemia (low blood calcium) and low blood potassium (hypokalemia).
Calcium, phosphorous, parathyroid hormone and vitamin D:
1) High phosphorous (hyperphosphatemia) – As the kidneys fail, they lose their ability to excrete excess phosphate leading to levels increasing in the blood. As calcium bonds with phosphorous, when levels increase, calcium levels drop in the blood. So, while there are typically no symptoms associated with high phosphorous levels, your cat may display symptoms of hypocalcemia (see below).
2) Low blood calcium(hypocalcemia) – Calcium is the most abundant mineral in the body, it provides strength to bones and teeth, nerve impulses, muscle contraction and blood clotting. As cats with kidney disease often have elevated phosphorous levels (hyperphosphatemia). As we have already discussed, calcium binds to phosphorous, so when phosphorous levels rise in the blood, calcium binds to it, which causes blood calcium levels to drop.
Symptoms of low blood calcium:
Neurological disorders such as twitching, facial rubbing, involuntary muscle contractions
Stiff legged gait
3) Vitamin D – Cats obtain vitamin D from sunlight and their food and is necessary for regulating calcium and phosphorous by controlling absorption from food and regulating parathyroid hormone. The kidneys convert vitamin D into its active form. When the kidneys are not functioning efficiently, they are less able to do so. As vitamin D levels drop which causes the parathyroid gland to over-compensate, which leads to pulling calcium out of the bones.
4)Weak bones – To compensate, the parathyroid gland secretes a parathyroid hormone which releases stored calcium in the bones. This calcium is what gives bones their strength. So as levels of stored calcium drop, the bones become weaker and more prone to breaking.
5) Low blood potassium (hypokalemia) – Hypokalemia is the most common electrolyte abnormality seen in cats with kidney failure. Potassium responsible for maintaining blood pressure, heart function and maintaining nerve, skeletal and muscle contraction. When potassium levels drop, the following can occur:
Muscle weakness and pain
Reluctance to move
Stiffness of the neck
6) Anemia – Cats with kidney disease often have a low red blood cell count due to the kidneys not producing enough erythropoietin to stimulate adequate red blood cell production. Symptoms of anemia include:
Pale mucus membranes
Loss of appetite
Rapid breathing (tachypnea)
How is kidney disease in cats diagnosed?
Your veterinarian will perform a thorough physical examination and take a medical history of your cat. He will palpitate the kidneys which may feel smaller in size. Some tests he/she may run include:
Complete blood count to evaluate for signs of infection, inflammation and anemia.
Biochemical profile. Blood urea nitrogen (BUN) and creatinine are waste products which are ordinarily excreted via the urine, in cats with kidney disease these products are not filtered out of the blood, causing levels to rise. High or low blood calcium, high phosphorous and high or low potassium may also be found.
Urinalysis will be able to provide additional information on the extent of kidney damage, urine-concentrating ability and if an infection is present in the urinary tract.
Urine specific gravity: This test is to check to see how concentrated the urine is.
Kidney ultrasound or X-ray to evaluate the kidneys and look for possible causes such as kidney stones, tumours or cysts and evaluate the size of the kidneys.
Kidney biopsy. This involves taking a small sample of the kidney for testing which can confirm chronic or acute kidney disease.
Symmetric dimethylarginine (SDMA): In the past, kidney disease was difficult to diagnose until a large percentage of nephrons had been lost. IDEXX have a new test known as Symmetric dimethylarginine (SDMA) which according to their site is a biomarker for kidney function and can detect kidney disease when 40% of kidney function has been lost which is considerably earlier than the standard 75% loss. More information can be found on the IDEXX site.
T3 and T4 tests for hyperthyroidism – Your veterinarian may also recommend testing your cat for hyperthyroidism as kidney disease and hyperthyroidism is also a disease of older cats and the symptoms can be similar and it is not uncommon for cats to have both hyperthyroidism as well as chronic kidney disease. Hyperthyroidism can mask the signs of chronic kidney disease because of increased blood flow to the kidneys. Treatment for hyperthyroidism is a balancing act if your cat has both hyperthyroidism and kidney disease. Most veterinarians will recommend putting your cat on thyroid medication such as Methimazole and Carbimazole instead of the standard radioactive iodine or surgery, which are both permanent. If your cat’s kidney disease becomes worse, the thyroid medication can be reduced or stopped.
Once your cat has been diagnosed with kidney disease it will be staged from 1 – 4, with 1 being the mildest and 4 being the most severe.
How is kidney disease in cats treated?
In some cases of acute renal damage, once the underlying cause has been treated, it may be possible to halt further damage to the kidneys. Sadly the mortality rate of cats with acute kidney failure remains high. So early intervention is a must.
Treatment of acute renal failure depends on the staging and is aimed at addressing the underlying cause (if one is found), stabilising the cat and helping the body to remove toxins. Acute renal failure is commonly caused by ingestion of toxins and it is always a medical emergency and hospitalisation will be required. As well as treating the underlying cause, the following will be necessary:
Fluids to correct dehydration and electrolyte imbalances.
Prescribe medications to treat high blood pressure.
Painkillers if necessary.
In some cases, dialysis may be necessary to remove toxins from the blood.
Some cats may recover but go on to develop chronic kidney disease due to the damage caused to the kidneys. Other cats may fully recover once the initial emergency has been treated and the kidneys supported while they recover.
There is no cure for chronic renal disease except a kidney transplant (see below), the goal of treatment is to slow down the progression of the disease, decrease the burden on the kidneys and manage symptoms.
Fluids: Administration of intravenous or subcutaneous (under the skin) fluids to treat dehydration and electrolyte imbalances as well as help the kidneys to flush out toxins from the body. Initially your cat may need to receive fluids in-house via IV, however, long term management of kidney failure may require further fluid therapy and many cat owners may need to learn how to give fluids subcutaneously at home (this is not as daunting as it sounds).
Encourage water intake – Avoiding dehydration is always better than treating it (above). Encourage your cat to drink water by feeding a wet diet, having multiple water bowls and different types in the home. Some cats like still water, others may prefer running water from a water fountain. If those don’t work, you could try flavouring the water by adding some of the water from a tuna can.
Prescription diet: These diets should consist of good quality but reduced protein and phosphorous. Cats need protein every day for growth, building muscles and repairing tissue. After the body uses the protein in the foods, a waste product called urea is made. Cats with kidney disease are not able to get rid of this urea normally. Damaged kidneys may not be able to remove phosphorus from the blood. This causes the level of phosphorus to become too high. A high blood phosphorus level may cause the cat to lose calcium from their bones. Popular kidney disease diets include Hills k/d and Royal Canin Veterinary Feline Renal. They come in both dry and canned form. Canned has the advantage of having a higher water count, in cats with chronic kidney disease, fluids are vital in helping the kidneys flush out toxins.
Appetite stimulants may be necessary as it is very common for a cat with CRD to become reluctant to eat. There are more tips on how to get a cat to eat here. Weight loss is a common problem in cats with chronic kidney disease and the goal is to assist them in gaining weight to healthy levels.
Feeding tube. If after coaxing and/or administration of appetite stimulants your cat still won’t eat, it may be necessary to have a feeding tube inserted.
Phosphorus binders: Phosphate is an abundant mineral in the body. Together, calcium and phosphate work closely to build and repair bones and teeth. Around 85% of phosphate is found in the bones, the remaining 15% is stored in the cells where it is responsible for energy metabolism as well as being an integral structural component of DNA and RNA. Excess phosphate is filtered by the kidneys and excreted in the urine. As the kidneys begin to fail, they are less able to get rid of excess phosphate, and levels begin to build up. A high blood phosphorus level may cause the cat to lose calcium from their bones. Your veterinarian may recommend phosphate binders in conjunction with a phosphate restricted diet to slow the progression of kidney disease.
High blood pressure (hypertension): As the kidneys are responsible for controlling blood pressure, cats with CRD are unable to do this properly and blood pressure can rise. This, in turn, causes further damage to the kidneys. Medications can help to reduce blood pressure such as calcium channel blockers, beta blockers, ACE inhibitors, and diuretics. The calcium channel blocker amlodipine is most often prescribed. Medications won’t cure high blood pressure but will assist in controlling it.
Antacids and anti-nausea medication.
Potassium supplements either orally or intravenously.
Calcitriol (vitamin D) may be necessary if your cat’s phosphorous and calcium levels have become unstable.
Erythropoietin: The kidneys produce a hormone known as erythropoietin, which instructs the bone marrow to produce red blood cells. Cats with kidney disease often have a low red blood cell count which can lead to anemia. Only the human form is available and some cats may eventually recognise this substance as foreign and antibodies will be created against it.
Iron supplements – For cats receiving erythropoietin, iron supplementation will be required due to an increased demand for iron during red blood cell production.
Regular monitoring. Your veterinarian will need to regularly check your cat’s blood pressure, hydration as well as running biochemical profile, complete blood count and urinalysis tests.
Kidney dialysis – Some veterinary practices may offer this service. A needle is inserted into your cat’s jugular vein and blood is passed through a dialysis machine which performs the same job as the kidneys to remove metabolic waste from your cat’s blood before returning it back into your cat. Each treatment can last several hours. Not many practices have this equipment, and when it is used, it is usually reserved for cats with acute renal failure or to keep a cat alive while he is prepared for a kidney transplant. A cat with chronic kidney disease would require repeat dialysis which is generally not practical.
A kidney transplant is relatively rare and not without its drawbacks, it is the only possible curative treatment for chronic kidney disease. Transplant surgery has to be performed by a veterinary specialist, many cats with chronic kidney disease are already extremely unwell and may not survive surgery and those who do may possibly reject the kidney at a later date. The procedure costs many thousands of dollars. Then there is the ethical dilemma of obtaining a kitten from a young donor cat who obviously can not give its consent. Most donors are sourced from animal shelters and will donate one of their kidneys. The conditions usually stipulate that the donor cat must be adopted by the family whose cat is receiving the kidney transplant. Donor recipients will need to be on immunosuppressive drugs for the rest of their lives to reduce the chances of rejection. Regular blood tests will be required for the remainder of the donor cat’s life.
Regular blood tests will be necessary to monitor your cat.
Administer medications as directed by your veterinarian.
You will need to closely monitor your cat’s health. Watch for signs of increased thirst and urination, decreased appetite and weight loss. If you notice any changes at all, please see your veterinarian.
Is it possible to prevent kidney disease?
I am not sure it is entirely possible to prevent chronic kidney disease, but there are steps we can take to reduce the chances or slow down progression. Cats are living longer than ever, and chronic kidney disease is a disease of older cats, so it stands to reason that we are seeing more of it now. There are ways to reduce your cat’s chances though.
Gum disease is a known cause of chronic kidney failure in dogs. Bacteria from the gums can be easily transported via the blood supply to the kidneys where they can cause damage. Maintaining proper dental hygiene in cats will reduce his chances of developing gum disease. If you do notice redness or bad breath in your cat, see a veterinarian as soon as possible. Gingivitis is the precursor to gum disease and caught early enough, it can be treated.
Feed a high-quality diet, preferably wet from kittenhood.
All cats should have an annual veterinary check up with routine screening tests taken. Cats older than 8 should have twice yearly examinations to pick up problems early. Work closely with your veterinarian, this is an extremely common disease in cats, and they have a huge amount of experience which will help you and your cat.
I know this is a lot to take in, chronic kidney disease is such a common disease and it deserves a detailed article. To quickly summarise:
Kidney disease occurs when the filtering units die and are not replaced. This means toxins build up in your cat’s bloodstream as well as other essential functions no longer being carried out.
Symptoms don’t present until 75% of kidney function has been lost.
Common symptoms include increased thirst and urination, weight loss, bad breath.
It may be acute or chronic. Acute is usually the result of toxins damaging the kidneys. Chronic is slow and progressive.
Treatment of chronic kidney disease is aimed at slowing down the progression of the disease with fluids, dietary changes and supplements where necessary.
This website has a wealth of information on chronic kidney disease.