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Noninfectious Diseases of the Urinary System of Cats

By Scott D. Fitzgerald, DVM, PhD, DACVP, DACPV, Professor, Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University
Joseph W. Bartges, DVM, PhD, DACVIM, DACVN, Professor of Medicine and Nutrition, The Acree Endowed Chair of Small Animal Research, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee
Scott A. Brown, VMD, PhD, DACVIM, Josiah Meigs Distinguished Professor and Head, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia
Sherry Lynn Sanderson, BS, DVM, PhD, DACVIM, DACVN, Associate Professor, Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia
Melissa S. Wallace, DVM, DACVIM,

Also see professional content regarding noninfectious diseases of the urinary system.

Not every disease is caused by infection with bacteria, viruses, or other outside agents. There are a variety of noninfectious disorders that can impair the urinary system. All of these diseases and conditions can be serious threats to the health of your cat.

Kidney Dysfunction

The kidneys’ most important function is to filter waste from the blood. When this does not happen properly, waste products can build to dangerous levels in the blood. This is called azotemia. Azotemia can be caused by many factors, including dehydration, congestive heart failure (see Heart Disease and Heart Failure in Cats), and shock. Azotemia can also occur as a result of urine not being able to flow properly through the urinary tract.

Chronic Kidney Disease and Kidney Failure

Longterm, or chronic, disease can damage the kidney so severely that it is not able to function properly. This happens slowly. Chronic kidney disease often continues for many months or years before a cat has any signs. There is rarely anything that a veterinarian can do to treat existing damage. Occasionally, chronic kidney disease results from a problem that is inherited or an abnormality present at birth. Some breeds of cats are more likely to have this problem (see Congenital and Inherited Disorders of the Urinary System of Cats); however, most of the time it is a problem related to old age. Starting at age 5 to 6, chronic kidney disease becomes more common, affecting up to 35% of elderly cats. Chronic kidney disease that is not inherited does not seem to be more common among certain breeds or among males or females.

Veterinarians classify chronic kidney disease into 4 stages based on laboratory tests and the results of physical examinations (see Table: Chronic Kidney Disease Stages). In Stage I, the kidneys are damaged but azotemia (a buildup of toxins caused by poor filtering of the blood by the kidneys) has not yet developed and the cat has no signs. This is the stage at which treatment has the greatest chance of success. However, because the cat has no signs, the disease is rarely diagnosed at this stage. In Stage II, the kidneys filter waste much more slowly than normal, and there is a buildup of waste chemicals in the blood, but most cats still have no signs. Signs that may be present at this stage include an increase in the amount of water in the urine and an increased volume of urine. In Stage III, filtering slows even more, the waste chemicals are more concentrated in the blood, and the cat develops signs of disease. Stage IV, the final stage, reflects continued kidney damage and accumulation of waste products in the blood. By this time, the cat feels and acts very sick.

Determining the cause of chronic kidney disease, especially in the early stages, will help determine the appropriate treatment and outlook for your cat. Some of the common causes include diseases of the circulatory system (such as high blood pressure, problems with blood clotting, and not having enough oxygen in the blood) or other diseases of the kidneys such as pyelonephritis (see Infectious Diseases of the Urinary System of Cats : Kidney Infection (Pyelonephritis)) or tumors. Whatever the cause, chronic kidney disease usually results in scarring of the kidneys, which gets gradually worse.

Cats usually have no signs of kidney disease until they are at Stages III or IV, when their kidneys are working at less than 25% of their usual capacity. Exceptions to this are cats with other illnesses that affect the entire body or kidneys that become unusually inflamed or sore and cause vomiting or pain. Veterinarians may be able to detect a problem in a blood test or on physical examination even before the cat develops signs of kidney failure. Usually, the earliest signs are excessive thirst and urination. However, these signs may signal other diseases as well, and they do not begin to appear until Stage II or III. After this, there are usually no new signs until Stage IV, when affected cats vomit and are sluggish. As the disease progresses over months, other problems begin. These include loss of appetite, weight loss, dehydration, sores in the mouth, vomiting, and diarrhea.

Chronic Kidney Disease Stages

Disease Stage

Physical Conditions



Stage I

Waste filtering slows. Waste chemicals start to appear in blood.

No easily visible signs. Laboratory or other tests required.

Identify and treat cause of kidney disease.

Stage II

Further slowing of waste filtering. Buildup of waste chemicals and imbalance of water in urine

Cat may be urinating more than previously. Tests show increased amount of waste chemicals in blood.

Treat underlying cause of the condition. A change of diet may be required (such as a low salt or other special diet).

Stage III

Kidneys often working at less than 60% of normal capacity.

Excessive thirst and urination

Support cat with kidney disease diet, monitor for infections, and treat underlying cause of kidney disease.

Stage IV

Kidneys working at less than 25% of normal capacity. Toxic chemicals build up in blood and affect other organs in the body.

Vomiting, depression, loss of appetite, weight loss, dehydration, mouth sores, diarrhea. Young cats may lose teeth. Bones can become soft and easily breakable.

Provide special diet. Treat underlying conditions. Provide comfort care. In severe cases, kidney dialysis or a kidney transplant might be possible.

To diagnose chronic kidney disease, veterinarians generally use a combination of x-rays, ultrasonography, urine and blood tests, and physical examination. These tests are also used to check the response to treatment and monitor complications related to the kidney disease.

With proper treatment, even cats with as little as 5% of normal kidney function can survive for a long time. The recommended treatment depends on the stage of disease. Identifying and treating complications, such as high blood pressure or urinary tract infections, needs to be done as well. All cats with kidney disease should see their veterinarian every 3 to 6 months, or more frequently if there are problems. During these visits, the veterinarian will do tests on the cat’s blood and urine.

In the later stages of kidney disease (III and IV), the cat should be taken to the veterinarian every 1 to 2 months. At this stage, treatments will focus on easing some of the signs of the disease. A commercial diet developed for cats with chronic kidney disease may be recommended, along with appropriate medications. Sometimes veterinarians will recommend intravenous fluids or feeding tubes. At this point, there are very few options. Dialysis machines, which do the job of the kidneys by filtering the blood, can prolong life, but dialysis is not feasible for most pets. A kidney transplant can be done, but requires immune-suppressing drugs to prevent the body from rejecting the new kidney, which can cause other problems.

Acute Kidney Disease

Acute kidney disease is the result of sudden, major damage to the kidneys. This damage is usually caused by toxic chemicals either consumed by your pet or built up by an abnormal condition in your pet’s body. Kidney function can also be affected when the kidneys do not receive sufficient oxygen, such as when a blood clot blocks the flow of blood to the kidneys.

Some cats may consume toxic chemicals, such as antifreeze, or poisonous plants that can damage the kidneys. There are many substances in the average home that may be safe for humans but dangerous for cats and other pets see Introduction to Poisoning. Some toxic chemicals come from inside the cat’s body. For example, a buildup of calcium or other substances can occur due to disease in another part of the body. The effects on kidney function can last from 1 to 8 weeks, depending on the chemical(s) that caused the injury.

Mild kidney disease often goes unnoticed. However, repeated occurrences can lead to chronic kidney disease. The 4 (I through IV) stages of acute and chronic kidney disease are the same (see Noninfectious Diseases of the Urinary System of Cats : Chronic Kidney Disease and Kidney Failure). Usually, acute kidney disease is not detected until Stage IV, when signs can include loss of appetite, depression, dehydration, sores in the mouth, vomiting, diarrhea, and urinating a smaller than normal volume of urine.

It is important to determine whether the kidney disease is acute or chronic, as well as the cause of the disease. This information will help your veterinarian determine the most appropriate treatment. If your veterinarian can determine what caused the kidney injury, treatment will be aimed at this cause. Cats that are dehydrated or not eating may require intravenous fluids or a feeding tube. If none of the available treatments work, and your cat is simply not producing urine, the only remaining options are kidney dialysis, a kidney transplant, or euthanasia.

Glomerular Disease

The glomerulus is one of the structures that are essential for kidney function. It is made up of special blood vessels that help filter blood. Each kidney contains thousands of these structures. Glomerular disease sometimes causes kidney disease in cats. Damage to parts of the glomerulus can cause protein in the urine and low levels of a protein called albumin in the blood. This can lead to other problems, such as swelling of the legs, high cholesterol, and blood clots.

The kidneys consist of an outer part (cortex) and an inner part (medulla). The nephrons filter the blood and produce urine.

Glomerular disease can occur due to the longterm effects of high blood pressure. However, glomerular disease can also occur as a result of other disorders such as hyperadrenocorticism (an excess of cortisol) or amyloidosis. Some glomerular disease is immune-mediated, that is, caused by the cat’s immune system attacking parts of its own body.

Disease in the glomerulus often leads to protein in the urine, low levels of protein in the blood, a buildup of fluid in the abdomen (which can cause visible swelling), shortness of breath, and swelling in the legs. Taken together, these signs are called the nephrotic syndrome. (“Nephrotic” means relating to the kidneys.) The loss of protein through the urine can cause loss of muscle tissue. Most cats with glomerular disease eventually develop Stage III or IV kidney disease. Kidney disease that is accompanied by protein in the urine often leads to high blood pressure.

Your veterinarian will look for increased levels of protein and other chemicals in your cat’s urine and blood. Physical examination usually reveals that something is wrong; however, the signs are often nonspecific and could point to any of a wide variety of problems.

A biopsy of the kidneys is often required to determine the cause of the glomerular disease. Additional tests may be required in some cases, including x-rays, ultrasonography, and special blood tests.

Treatment for glomerular disease varies according to the underlying cause. In addition, kidney failure should be treated with appropriate medications (Veterinary.heading on page Noninfectious Diseases of the Urinary System in Dogs : Glomerular Disease).

Feline Idiopathic Cystitis and Feline Interstitial Cystitis

Feline idiopathic cystitis is an inflammation of the urinary bladder of unknown origin. This condition has also been called idiopathic feline lower urinary tract disease (idiopathic FLUTD) and feline urologic syndrome. The cause is unknown, but certain factors such as viral infections, stress, diet, and genetic factors may play a role. Both male and female cats are affected.

Signs of feline idiopathic cystitis include frequent urination, blood in the urine, straining or distress while urinating, and urination in inappropriate locations. A urinary tract obstruction may occur in male cats due to their longer and narrower urethras; this should be considered a medical emergency and requires immediate veterinary attention. Signs of this condition include frequent unsuccessful attempts to urinate, lethargy, loss of appetite, and reluctance to move.

Diagnosis depends on a complete history and physical examination, as well as appropriate laboratory tests to identify feline idiopathic cystitis and exclude other conditions. These may include urinalysis and bacterial culture of urine, blood tests, x-rays, ultrasonography, and cystoscopy.

Treatment of this condition has many approaches. If bacteria are identified, antibiotics will be prescribed. Drugs that reduce pain and inflammation may be useful in some cases. Cats should have access to plenty of fresh, clean water to encourage water intake (so the cat will have less concentrated urine). Changing from a dry to a canned food may also help add water.

Another condition that may be related to—or the same as—feline idiopathic cystitis is called feline interstitial cystitis. Currently, it is unclear whether these are 2 separate conditions or whether they represent the same overall disorder. Signs of both conditions are similar and both involve inflammation of the bladder with bladder pain, straining, and bloody urine.

Renal Tubular Problems

Renal tubules are structures in the kidneys that help filter blood. Healthy kidneys help the body to get rid of acid by producing urine that is very acidic. Diseased kidneys cannot get rid of acid properly, and instead of being eliminated in the urine, this acid builds up in the blood, leading to a condition called uremic acidosis. This condition can also occur when there are defects in the renal tubules, in which case it is called renal tubular acidosis. These defects are rare in cats. Treatment may involve medications to rebalance the amount of acid in the blood.

Obstructions of the Urinary Tract

Even when the kidneys are functioning normally, a blockage in the urinary system at any point below the kidneys can lead to a backup of toxic wastes that can damage the kidneys and cause illness. In cats, the most common cause is a “plug” composed of protein, cellular waste, and/or crystallized minerals that blocks the urethra. Other possible causes include urinary tract stones (see Noninfectious Diseases of the Urinary System of Cats: Urinary Stones (Uroliths, Calculi)), tumors, or blood clots in the ureters or urethra.

If the flow of urine is blocked, the kidney becomes abnormally enlarged. When this happens suddenly to both kidneys, especially when the urine is completely blocked, the cat does not live long. When the blockage is only partial, or only occurs on one side, the cat often survives but the kidneys may sustain permanent damage. The affected kidneys eventually become giant, useless urine-filled sacs and may become infected. The ureter may also become enlarged due to a backup of urine. This often occurs when the blockage is located further down the urinary tract and away from the kidneys.

Cats with a urinary blockage will attempt to urinate frequently. These attempts, however, may be painful and will result in only small amounts of urine being produced. Often, blood will be present in the urine. An affected cat may have a painful abdomen, lose interest in food, and become more and more depressed. As the condition progresses, the cat may vomit and become dehydrated. Your veterinarian will be able to readily diagnose urinary tract obstructions based on the signs and a physical examination.

To restore normal urine flow, the blockage must be removed. In most cases, intravenous fluids will be used to restore the balance of various chemicals in the blood. Surgery is often required to resolve the blockage of the urinary tract.

If a cat has signs of a blocked urethra, it is critical to seek veterinary care immediately. Cats with a complete blockage may die within 2 to 3 days without treatment.


Tumors that originate in the kidneys and urinary tract are not common in cats. Tumors can be benign (harmless) or malignant (cancerous). Benign tumors, such as fatty tumors or tumors made of fibrous tissue, are usually discovered only by accident and do not require treatment.

Cancers that begin in other parts of the body may spread to the kidneys. (When cancer spreads from one organ to another, it is said to metastasize and the cancer itself is described as metastatic.) Metastatic tumors can appear on one or both kidneys. Lymphosarcoma is the type of tumor that most commonly spreads to the kidneys. Up to half of cats with cancer of the lymphatic system also develop cancer in their kidneys. In some cases, the cancer remains only in the lymph tissues and the kidneys; in others it also spreads to the brain. When cancer spreads to the kidneys, it usually takes the form of many small tumors. It can affect both kidneys and may cause the kidneys to become unusually large and irregularly shaped. Lymphosarcoma in cats frequently occurs along with infection with the feline leukemia virus.

Signs of kidney tumors are usually general and can point to many different illnesses. Common signs include weight loss, poor appetite, depression, and fever. Your veterinarian will need to eliminate other causes of these signs before confirming cancer. Occasionally, tumors that appear in both kidneys can cause enough damage that the cat will develop signs of late-stage kidney disease (see Noninfectious Diseases of the Urinary System of Cats : Chronic Kidney Disease and Kidney Failure).

Your veterinarian may suspect a tumor of the kidneys based on physical examination and careful consideration of your cat’s signs in the weeks and months prior to becoming ill. This suspicion can be confirmed with ultrasonography, x-rays, or contrast x-rays of the urinary tract. Cancer cells can also occasionally be found in the urine. A biopsy of the tumor is usually necessary to determine its type.

Normally, kidney tumors must be surgically removed. Usually it is necessary to remove the entire affected kidney. Tumors in the lymph nodes around the kidney are usually treated with chemotherapy instead of surgery. If your cat develops a urinary cancer, your veterinarian will assess the severity of your pet’s condition, the outlook for your pet, and other factors when recommending a treatment program. (For a more detailed discussion of tumors of the kidney and urinary tract, see Noninfectious Diseases of the Urinary System in Dogs : Tumors.)

Problems with Urination

Urination problems can be grouped into problems with storing urine and problems with eliminating urine. Urinary incontinence is the inability to prevent or control urination. Incontinent animals leak urine constantly or occasionally without realizing it. An incontinent cat may leave a pool of urine where it has been lying or dribble urine while walking. The fur around the vulva or penis may be wet, and the constant dribbling of urine can cause inflammation and urine scalding of the skin in these areas.

Problems with Urine Storage

Problems with urine storage are identified by inappropriate leakage of urine. They can be caused by several different conditions, including failure of the muscles in the bladder to relax appropriately, injury or damage to the urethra or other parts of the urinary system, and overflowing of the bladder.

Urge incontinence occurs when urine leaks during the times when an animal feels the urge to urinate as opposed to urine that leaks when an animal is unaware of it. Urge incontinence is usually caused by irritation of the bladder muscle that forcibly expels the urine. This is usually due to inflammation of the bladder. Problems with the urethral sphincter (the muscle that opens and closes to allow urine to pass through the urethra), can also cause this type of incontinence.

Incontinence that results from birth defects or malformation of the urinary system usually becomes obvious while the cat is young. For example, a cat that was born with an ectopic ureter (see Congenital and Inherited Disorders of the Urinary System of Cats : Ectopic Ureter) on one side might urinate normally but dribble urine on and off, whereas cats with ectopic ureters on both sides are less likely to be able to urinate normally at all.

Problems with Urine Elimination

Problems with urine elimination can have many causes, including physical blockage of the urethra by stones, growths, or scar tissue; a lack of muscle tone in the muscle that expels urine; or problems related to the nervous system. Cats that cannot urinate normally will usually try to urinate often, but the urination will be slow and painful and only a small amount of urine will come out. Cats with urine elimination problems may also develop incontinence over time; if the bladder does not empty properly, it can become stretched out and begin to overflow and leak.

Neurologic Problems

Problems with urination can sometimes be caused by damage or disease that affects the brain or spine, damage to the major nerve in the pelvis that connects to the bladder, or a lack of muscle tone in the muscle that controls urination. Dysautonomia is a condition in cats in which the nervous system does not work properly. It can also lead to urinary incontinence. Cats with any neurologic urination problem may develop incontinence over time if the bladder becomes too full and begins to overflow and then leak.

Diagnosis and Treatment of Urination Problems

A thorough physical examination and a history of the cat’s behavior can help your veterinarian determine whether your cat has problems related to urination. Your veterinarian will probably also want to watch your pet urinate. Specialized tests, such as ultrasonography, x-rays, or neurologic tests, may be helpful in some cases.

Treatment of urination problems will vary depending on the cause. Urethral incontinence can be treated with medication that targets the membrane inside the urethra (called alpha-adrenergic agonist drugs). Urge incontinence can be treated with medication that targets certain nerves (called anticholinergic drugs). Weakened bladder muscles can be treated with medications that target slack muscles (called cholinergic drugs). Muscle relaxants may be useful in cases where muscle coordination issues are identified.

In cats in which the bladder has lost its muscle tone due to neurologic problems, there are few medical options to restore muscle tone. It is usually necessary to empty the bladder with a catheter several times a day for the rest of the animal’s life. In these cases, you will need to be trained to properly insert and remove the catheter.

Urinary Stones (Uroliths, Calculi)

Uroliths are stones (also known as calculi) formed when minerals that naturally occur in urine clump together to form tiny crystals. These stones can develop anywhere in the urinary system, including the kidney, ureter, bladder, or urethra. Certain types of stones appear to have increased in cats in recent years. The cause is not clear, but researchers are looking at the effects of diet to determine if there is any link.

Veterinary researchers do not completely understand what causes stones to form (see Why Cats Develop Uroliths (Stones)). There are many different types of stones, each formed from a complex mixture of various minerals, and each of which develops only under certain conditions. They can be caused by a problem with the minerals themselves or by a problem with other chemicals that exist in urine and which, under normal circumstances, prevent stones from forming. The environment of the urinary tract may also contribute to stone formation. All of these conditions can be affected by urinary tract infections, diet, digestion, the amount of urine that a cat produces, how frequently a cat urinates, medications, and genetics.

Cats with very tiny stones in the urinary system do not usually have any signs. However, larger stones in the lower urinary tract may interfere with urination or irritate the lining of the urethra. In turn, these problems can cause an inability to urinate, blood in the urine, and slow or painful urination. Kidney stones (which are rare in cats) usually cause no signs unless the kidney becomes inflamed or the stones pass into the ureter. If a ureter becomes blocked by a stone, it can cause vomiting, depression, or pain in the abdomen in the area around the kidneys. Such pain is particularly common when both ureters are suddenly and completely blocked; the fluids back up causing the kidneys to become enlarged. Pain is the only sign of stones in the ureter on only one side; however, pain can be difficult to detect in cats. If the blocked ureter is not diagnosed right away, kidney damage occurs. Ultimately, the blocked kidney is destroyed.

Veterinarians can sometimes detect stones in the bladder by pressing on the cat’s abdomen. Stones in the urethra may also be detected during a rectal examination or when attempting to insert a catheter. There may be many stones present at once. If one stone is located, it is important to examine the entire urinary tract to look for others. X-rays can detect stones as small as 3 millimeters in size. Your veterinarian will also perform tests on the cat’s urine and may need to do ultrasonography or other specialized tests.

Treating stones, and preventing their return, depends on their type and location. Treatment and prevention may include surgery, a special diet, and medication. When stones are removed, your veterinarian may send them to a laboratory to be analyzed. Knowing what types of minerals are in the stone can provide the information needed to prescribe medication that can prevent the formation of more stones. Cats undergoing treatment for uroliths will need to be monitored closely, returning at regular intervals for additional testing.

Also see professional content regarding noninfectious diseases of the urinary system.

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