Pyelonephritis in Cats

  • Author:

  • Pyelonephritis is an inflammation of the renal pelvis (a hollow area in the centre of the kidney) renal parenchyma (the solid part of the kidneys) due to a bacterial infection (and less often viral or fungal infection).

    The urinary tract consists of the upper and lower sections. The upper urinary tract (UUT) is made up of the kidneys and the ureters, tubes propel urine from the kidneys to the bladder. The lower urinary tract (LUT) includes the bladder, which stores urine and the urethra, which is the thin tube that carries urine from the bladder and out of the body.

    Infection typically occurs when bacteria (most commonly Escherichia coli and Staphylococcus spp., less common bacteria include Proteus, Streptococcus, Klebsiella, Enterobacter, and Pseudomonas aeruginosa) ascend from the bladder, along the ureters, and into the kidney. Less common is hematogenous spread, where an infection elsewhere travels through the bloodstream to the kidneys. It can be acute (sudden onset) or chronic (longstanding).

    Normally the upper urinary tract is protected by the cat’s normal defence mechanisms:

    • The one way flow of urine through the ureters from the kidneys to the bladder.
    • Bladder epithelial cells which line the inner surface of the bladder secrete antibacterial peptides to clear the bladder.
    • The acidic pH of urine, as well as high osmolality, inhibits the growth of bacteria.

    Risk factors include recent lower urinary tract infection, congenital abnormalities or kidney stones that obstruct urinary flow, impaired immune system, diabetes (which can cause glucose in the urine), hyperadrenocorticism (Cushing’s Syndrome), steroid administration, urethral catheterisation, urine retention, urinary tract neoplasia, and chronic renal (kidney) disease which results in dilute and altered urine composition.


    Some cats will be asymptomatic (no symptoms), however, when they are present, they can include:

    Pyelonephritis can lead to renal cell death and chronic renal insufficiency (CRI). Immediate veterinary attention is necessary to treat the condition. Signs of CRI include vomiting, increased thirst and urination, metabolic acidosis and non-regenerative anemia.


    The veterinarian will perform a physical examination of the cat and obtain a medical history from you. During the evaluation, the kidneys may be painful upon palpitation. It will be necessary to perform tests to confirm the diagnosis.

    Baseline tests: Complete blood count, biochemical profile and urinalysis.

    • Urinalysis may reveal protein, bacteria, blood, and pus in the urine. The veterinarian may send the urine sample to a veterinary laboratory for culture and sensitivity.
    • Biochemical profile may be normal or may reveal azotemia (elevation of blood urea nitrogen and serum creatinine levels).
    • Complete blood count may show an elevated white blood cell count (leukocytosis) and anemia.

    Imaging: Ultrasound or x-ray which may reveal increased kidney size (renomegaly), a dilated (enlarged) renal pelvis and stones if present.

    Pyelocentesis: Ultrasound-guided aspiration of fluid from the renal pelvis which will be cultured to identify any bacteria present.

    Histopathology: Evaluation of a biopsy of the kidney.


    The goal of treatment is to address the underlying cause as well as treat the infection. This will include:

    • Antibiotic therapy: Broad-spectrum IV antibiotics followed by oral antibiotics for 4-6 weeks. The antibiotic choice will be based on the results of culture and sensitivity.
    • Stone dissolving diets: Hills c/d may be prescribed for small struvite stones.
    • Surgery: To remove larger stones or stones such as calcium oxalate which cannot be dissolved with diet.
    • Symptomatic treatment: Additional therapies to manage symptoms which can include anti-nausea medication, fluids to treat dehydration and correct electrolyte imbalances, and nutritional support.


    • Julia Wilson, 'Cat World' Founder

      Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio