At a glance
About: Kidney disease occurs when the kidneys lose their ability to filter the blood efficiently. The disease can be chronic (slow and progressive) or acute (sudden onset). As the kidneys fail, toxins build up in the blood.
Diagnosis: Routine blood tests along with a kidney ultrasound and additional tests, where necessary.
Treatment: Address the underlying cause in cats with acute kidney failure, for chronic kidney disease increasing fluid intake, prescription diet, phosphorous binders and supplements where necessary.
Kidney disease 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 which cause metabolic wastes to build up in the blood.
Cats have two bean-shaped kidneys. They are remarkable at adapting to decreased numbers of nephrons, and it is only when 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 chronic kidney disease, which occurs in cats over ten 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 essential functions of the kidneys:
- 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 the 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.
There are many causes of kidney disease in cats. Because the kidneys filter the blood, other diseases and infections can damage the kidneys.
Acute Kidney Failure/Injury (Acute Renal Failure or ARF):
Acute kidney failure is brought about by a sudden decline in kidney function. 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 ingestion, snake bite, pesticides, ingestion of human medications, especially NSAID’s such as Ibuprofen (Nurofen/Advil)
- Heart failure
- Heatstroke (hyperthermia)
- Kidney stones (which can lead to a blockage)
- Sepsis (blood infection)
- Disruption of blood flow to the kidneys
Chronic Kidney Disease (CKD)
This type of kidney disease is slow and progressive occurs most often in senior cats. Veterinarians still aren’t 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.
- Cystitis – Inflammation of the bladder.
- 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 – Due to chronic renal disease.
- 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 can replace lost or damaged cells (such as the liver), however, kidneys are not able to make new nephrons.
Excessive thirst and urination and are the hallmarks of kidney disease. Always speak to 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, which leads to excessive loss of water. 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 sick, 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:
- Weight loss
- Bad breath
- Mouth ulcers
- 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 his final two days, he would sit hunched over his water bowl but not drinking. At this point, he had developed severe uremic poisoning.
Effects on the body
The impact of kidney disease affects many body systems.
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.
High phosphorus (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 signs of hypocalcemia (see below).
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 phosphorus levels (hyperphosphatemia). As we have already discussed, calcium binds to phosphorous, so when phosphorus levels rise in the blood, calcium binds to it, which causes blood calcium levels to drop.
Vitamin D deficiency:
Cats obtain vitamin D from sunlight and their food, and it is essential 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.
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.
Low blood potassium (hypokalemia):
Hypokalemia is the most common electrolyte abnormality to develop in cats with kidney failure. Potassium is 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
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 mucous membranes
- Weight loss
- Loss of appetite
- Rapid breathing (tachypnea)
- Generalised weakness
- Excessive sleeping
Your veterinarian will perform a thorough physical examination and take a medical history of your cat. He will palpate the kidneys which may feel smaller than normal.
Complete blood count: A blood test which measures the cells of the blood to evaluate for signs of infection, inflammation, and anemia.
Biochemical profile: A range of tests that measure the constituents of the plasma or serum component of the blood. 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: This test on a urine sample 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 compares the density of a sample of the cat’s urine to water and is useful for evaluating how well the kidneys are diluting urine.
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: A small sample of the kidney is taken and tested. This can confirm acute or chronic kidney disease.
Symmetric dimethylarginine (SDMA): In the past, kidney disease was difficult to diagnose until a large percentage of nephrons had been lost. IDEXX has 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: The 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.
Once your cat has been diagnosed with kidney disease it will be staged from 1 – 4, with 1 being the mildest and 4 the most severe.
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.
The goal of treatment for acute kidney disease is to address and treat the underlying cause and stabilise the cat. 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.
- Anti-nausea medications.
- 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 addressed 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.
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.
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 (urea) is produced. 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, which 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.
It may be necessary as it is very common for a cat with CRD to become reluctant to eat due to nausea. 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.
A feeding tube will be necessary if the cat still won’t eat despite coaxing or appetite stimulants.
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, and 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 start 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 restricted phosphate diet to slow the progression of kidney disease.
Manage high blood pressure:
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. Medications won’t cure high blood pressure but will assist in controlling it.
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.
Feline kidney transplants are rare and not without risk; however, it is the only possible curative treatment for chronic kidney disease. A veterinary specialist must perform transplant surgery. Most cats with chronic kidney disease are already extremely unwell and may not survive the surgery, and those who do may reject the kidney at a later date.
The procedure costs several thousand dollars, and there is the ethical dilemma of obtaining a kidney from a young donor cat who obviously can not give its consent. Most donors are sourced from animal shelters and will donate one kidney. 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 take immunosuppressive drugs for the rest of their lives to prevent rejection of the donor organ.
Potassium, calcitriol (vitamin D) and iron may be prescribed.
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.
Treatment of kidney disease is a team effort. You will work closely with your veterinarian. Day to day treatments are the responsibility of the caregiver; however, your veterinarian will need to check your cat’s blood pressure regularly, hydration as well as running biochemical profile, complete blood count and urinalysis tests.
Administer medications as directed by your veterinarian.
You will need to monitor your cat’s health closely. Watch for signs of increased thirst and urination, decreased appetite and weight loss. If you notice any changes at all, please see your veterinarian.
It is not 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 it is possible to treat if caught early.
Feed a high-quality diet, preferably wet from kittenhood.
All cats should have an annual veterinary checkup 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 a prevalent disease in cats, and they have a huge amount of experience which will help you and your cat.