While urinary tract infections (or UTIs) are relatively common in dogs, they are much less prevalent in cats. Of these UTIs, bladder infections are more commonly encountered. Infection involving the kidneys, on the other hand, is very uncommon in both species, especially in cats.

Although kidney infection in cats is overall rare, it can quickly become critical to a cat’s health if left untreated. Therefore, proper detection and prompt treatment are imperative at preventing severe complications, such as kidney failure. 

Pet parents should monitor their cats for the signs of a kidney infection, which can sometimes be subtle, and seek veterinary care if ever in doubt. Here is what you need to know about kidney infection in cats.

What Is a Kidney Infection?

The cat urinary tract is comprised of the lower urinary tract and upper urinary tract. The urethra (the tube connecting the bladder to outside the body to facilitate urination) and the urinary bladder make up the lower tract. The upper tract includes the ureters (the thin tubes connecting the bladder to each kidney) and two kidneys. The primary function of the kidneys, located on each side of the lower back, is to control fluid and electrolyte balance in the body, as well as to filter out blood toxins and other waste to produce urine. Urine travels from the kidneys through the ureters to the bladder and then is excreted through the urethra.

Kidney infections—termed pyelitis or, more commonly, pyelonephritis, depending on the area of the kidney affected—are a type of upper urinary tract infection, also termed a deep infection of the urinary tract. The causes and symptoms of kidney infection in cats and dogs are quite similar to the same condition in humans. Only one or both kidneys may be affected. 

When infection of the kidneys occurs, kidney (aka renal) function becomes impaired. Therefore, hasty diagnosis and therapy is essential to preserve your cat’s renal health.

What Causes Kidney Infections in Cats?

Like bladder infections, nearly all kidney infections in cats and dogs are caused by bacteria from the perineal region, mainly from fecal material from the gastrointestinal tract or else bacteria on the skin that enter the urinary tract through the urethral opening. The most common bacterial strains include Escherichia coli and Staphylococcus pseudintermedius, as well as various species of Proteus, Klebsiella, Enterococcus, Streptococcus, Enterobacter, and Pseudomonas. Urinary tract infections by anaerobic bacteria, fungi, parasites, or algae are extremely rare.

When kidney infections do arise in dogs, older canines are affected more frequently. However, no age predisposition regarding kidney infections has been established in cats. As in dogs, female cats may be at increased risk of UTIs due to the closer proximity of the female urethra to the anus, which allows for increased contact with bacteria that can enter the bladder and then spread to the kidneys.

While one-off (i.e. uncomplicated) bladder infections can occur relatively commonly in otherwise healthy female dogs, urinary tract infections in cats of both sexes and male dogs tend to only arise due to an underlying complication that impairs the animal’s normal host defenses against such infection. Acute (or sudden) causes of kidney infections in cats are rare. Typically, feline kidney infections stem from an underlying chronic condition.

Risk factors for kidney infection in cats include:

Abnormal anatomy of the urinary tract, such as:

• Stones of the urinary tract (uroliths) or mucus plugs, which may cause urinary obstruction
• Cancer of the urinary tract (neoplasia)
• Abnormal positioning of the ureter and the bladder (ectopic ureters), causing abnormal draining of urine
• Abnormal development of the kidneys (renal dysplasia)

Damage to the urethral sphincter, which increases the likelihood of bacteria entering the urethra

Inability of the bladder to empty fully (for example, neurologic impairment secondary to intervertebral disc disease, or IVDD)

Immunodeficiency (decreased immune system function): can be caused by diseases such as feline leukemia virus (FeLV); may also be secondary to the use of chemotherapeutic drugs or chronic glucocorticoid steroid use

Urine flow problems: for example, disorders that cause a slowing or stoppage of urinary flow (urine stasis) or a stream of urine to abnormally backflow up into the ureters from the bladder (vesicoureteral reflux)

Impaired renal blood flow

Concurrent systemic disease, such as:

• Chronic kidney disease (CKD) or chronic renal failure (CRF): Pyelonephritis
• Diabetes mellitus: Diabetics may have excessive glucose (sugar) in urine, which can promote excessive growth of bacteria. 
• Hyperthyroidism
• Feline lower urinary tract infection (FLUTD), which can be complicated by multiple conditions, including obesity

Post-operative complications, such as suture material left in the bladder following bladder surgery (cystotomy) or due to previous urinary catheterization

While the majority of kidney infections in cats arise from ascending bacteria from a bladder infection, infection elsewhere in the body can spread through the bloodstream to travel to the kidneys. Such infections may be secondary to infection of the lining of the heart (endocarditis), infection of the spinal discs (discospondylitis), abscesses, or severe dental disease.

Cat Kidney Infection Symptoms

While lower urinary tract infections, or bladder infections (also termed cystitis), present as localized signs to the lower abdomen and bladder, kidney infections can present as systemic signs, meaning the whole body can appear ill.

Acute renal infection is very uncommon in cats but may present as the following clinical signs:

• Lethargy
• Depression
• Dehydration
• Fever
• Abdominal and renal pain

Chronic kidney infection is more common, but its symptoms are often subclinical in cats, meaning signs may be vague or confined only to recurrent lower urinary tract infection signs. Signs include:

• Weight loss
• Decreased appetite
• Vomiting
• Increased urination and water consumption (termed polyuria and polydipsia, respectively, or PU/PD)
• Recurrent lower urinary tract infection signs, such as inappropriate litter box use (i.e. urinating outside the litter box, or periuria); urinating small amounts frequently (pollakiuria) or slow urination; pain upon urinating (stranguria), which may manifest as straining or vocalizing while urinating; blood in urine (hematuria) or urine discoloration; foul-smelling urine; and urethral discharge

Without speedy diagnosis and treatment of kidney infection in cats, acute kidney injuries can lead to chronic injuries. In turn, this can lead to chronic kidney disease, in which the kidneys inevitably shut down. If detected acutely, kidney injury can be healed. However, chronic disease can only be managed and its progression slowed, yet the damage already incurred cannot be reversed. Therefore, chronic kidney disease must be properly managed for the rest of the affected cat’s life.

Additional potential consequences of kidney infection are septicemia and sepsis, in which bacteria from the kidneys or their toxins enter the bloodstream, respectively, leading to severe systemic illness. Organs such as the heart, liver, and joints may be affected. Abscessation of the kidney can also occur. Furthermore, urosepsis can arise secondary to an obstruction blocking the outflow of urine from the kidneys, thus allowing decomposed urine to enter the bloodstream, also leading to further sickness.

As eventual death is a potential consequence of unmanaged kidney infections, swift diagnosis and treatment by your veterinarian are necessary.

Diagnosing Kidney Infection in Cats

Because a cat’s symptoms of kidney infection can be so vague, diagnosis can sometimes be difficult, especially when differentiating a kidney infection from a bladder infection. Therefore, your veterinarian will implement a combination of the following to fully diagnose a kidney infection. Like puzzle pieces, the findings of these tests each reveal a bit of the picture to assist your veterinarian in diagnosing a kidney infection.

Physical examination: A thorough physical exam with a good history of your cat’s recent behavior is the best initial tool to aid your vet in reaching a diagnosis. In the face of a kidney infection, your vet will detect pain upon kidney and bladder palpation, a thickened bladder, and possible enlarged kidneys (renomegaly). A fever and dehydration may also be observed.

Urinalysis: A urine sample, ideally obtained via direct sampling from the bladder with a sterile needle passed through the skin of the lower abdomen into the bladder (cystocentesis), is imperative to diagnose any urinary tract infection. With a UTI, the following are typically encountered: blood (hematuria), bacteria (bacteriuria), white blood cells (pyuria), and possibly cells from damaged kidneys (renal casts) in the urine. Following treatment, a urinalysis should be repeated regularly to monitor urine specific gravity (USG), an indication of kidney function, to ensure long-lasting kidney damage has not occurred.

Urine culture and sensitivity: To properly diagnose a kidney infection, urine should be cultured to determine what type of bacterial species are growing and to what antibiotics they are susceptible. A urine culture should be performed ideally at the time of initial testing, 5-7 days after antibiotics are started, 7-10 days after antibiotics are finished, and then possibly 1, 3, and 6 months later.

Blood work: Depending on the severity of your cat’s clinical signs, your vet may recommend blood work, especially if kidney damage is suspected. Blood work may reveal elevation of nitrogen waste products in the blood (azotemia) due to dehydration or kidney impairment, increased potassium and phosphorus, and elevated white blood cell count secondary to infection (neutrophilia).

Infectious disease testing: Your vet may suggest testing your cat’s blood for feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) to rule out these viruses, which can cause immunodeficiency and predispose a cat to other infections, such as pyelonephritis.

Abdominal radiographs: X-rays of the urinary system may be performed to observe the size and shape of the kidneys as well as check for the presence of any masses or stones. Your vet may take special X-rays via an excretory urography study, in which contrast is used to help highlight features of the renal system.

Abdominal ultrasound: Abdominal ultrasound scans the urinary tract for not only stones, signs of obstruction, and cancer, but also analyzes the structures within the kidneys. Dilation of the renal pelvis, the area of the kidney that funnels waste contents into the ureters, is a strong indication of a kidney infection.

Blood pressure measurement: If your cat has sustained chronic kidney damage, a blood pressure reading may be performed to rule out high blood pressure (hypertension). If your cat is severely ill and in shock, low blood pressure (hypotension) may occur.

The only definitive means of diagnosing kidney infection in cats is to perform invasive kidney testing—such as direct sampling of urine from the renal pelvis (pyelocentesis) or renal biopsy—which differentiate an upper urinary tract infection from one of the lower urinary tract. However, due to the high risk of potential severe complications caused by such tests, they are not recommended. Thus, diagnosis is typically made based on supportive findings of the tests discussed above.

Cat Kidney Infection Treatment

Regardless of severity, all kidney infections in cats, dogs, and humans require treatment. 

Proper treatment includes appropriate antibiotic use as determined by your veterinarian. Fortunately, the majority of cats are able to receive antibiotics as outpatient therapy. However, severe cases, such as those with septicemia, may require hospitalization with intravenous (IV) fluids and IV antibiotics (such as ampicillin).

Outpatient care includes proper compliance to your veterinarian’s instructions for antibiotic therapy in order to prevent persistent or recurrent infection and to help prevent antibiotic resistance. The most common antibiotics used in cats include oral amoxicillin/clavulanic acid (such as Clavamox) or injectable cefovecin (Convenia). Oral antibiotics such as marbofloxacin (Zeniquin) or pradofloxacin (Veraflox) are reserved for more severe infections. 

Oral antibiotics are typically prescribed to be used 2 to 3 times daily (every 8 to 12 hours) for 4 to 6 weeks. If urinary stones are present, antibiotics will be prescribed to be used until 2 weeks following the resolution of the stone. Once your veterinarian receives your cat’s urine culture and sensitivity results, initial antibiotic choice is subject to change. An appetite stimulant may also be prescribed on a short-term basis if your cat has not been eating well.

In addition to treating the kidney infection, your cat’s underlying concurrent disease predisposing him or her to such infection should be treated or else the kidney infection will not clear or will return. For instance, surgery, shock wave therapy (lithotripsy), or a prescription dissolution diet may be required for urinary stones. Surgery may also be required if your kitten has ectopic ureters. Additionally, systemic diseases such as kidney disease, diabetes mellitus, hyperthyroidism, and feline lower urinary tract disease must all be appropriately managed to prevent recurrence.

For very severe cases in which kidney necrosis or abscessation has developed, surgical removal of the affected kidney (nephrectomy) may be required.

After-care for any sustained kidney damage is also required, such as a special prescription renal diet (low in phosphorus, reduced in protein quantity but of increased quality, and higher in omega-3 fatty acids). Maintaining proper hydration will also be important.

Home remedies for kidney infections in cats are not recommended, as none have been proven to be fully effective. Additionally, some can be dangerous, and delaying prescription treatment can lead to worsening disease that can progress to kidney failure and death.

The cost of diagnostics and therapy can run from several hundred dollars to over $1,000. Therefore, a pet emergency savings account and pet insurance are important to have in advance to help offset costs.

The prognosis of feline kidney infection is usually good if caught and managed early. Recurrent kidney infections in cats can be much more difficult to manage and, thus, carry a more guarded prognostic outlook. If chronic kidney damage has already occurred, the prognosis is much worse. Therefore, prompt care by your local veterinarian is vital for your cat’s outcome.

How to Prevent Cat Kidney Infections

Pet parents can help prevent kidney infections from arising in their cats by keeping in tune with their cat’s health and tracking any behavior changes that may be a harbinger of illness. Since kidney infections in cats stem from another underlying disease, treating the predisposing disorder is key to helping reduce the likelihood of kidney infection. Therefore, adhering to your vet’s advice regarding chronic disease management is key.

Additionally, aiding your cat in maintaining a healthy weight is important, as obesity has been linked to a variety of health conditions, including diabetes mellitus and feline lower urinary tract disease, which, in turn, can increase the risk of pyelonephritis upstream. 

Moreover, proper dental hygiene is also important to prevent the showering of the bloodstream with bacteria, which can migrate to the kidneys.

Safeguarding urinary health is also important for cats. This includes proper litter box maintenance, including good hygiene as well as having a sufficient number of litter boxes for the cats in your household (the 1+1 rule is recommended, in which each cat has his or her own litter box plus one extra for the group). 

Hydration is also important, so encouraging your cat to drink more with a water fountain or increasing water intake with canned wet food is recommended. Water helps keep the urinary tract happy and increases urinary voiding, which helps rid the urinary tract of bacteria and helps prevent them from colonizing the lining of the urinary tract. 

Your vet may also suggest a prescription urinary diet and can guide you on tips to keep your cat at a healthy weight. 

Finally, environmental enrichment is important by reducing stress and the risk of cystitis in your cat; such tips include play time and mental stimulation. Cranberry extract supplements may help in theory, but their efficacy has not been fully evaluated in cats.

Fortunately, kidney infections in cats are very uncommon, and hopefully, your cat will never develop one. But if it does occur, you will be well equipped to assist your vet in quickly diagnosing and treating your cat.