Feline Pyelonephritis

Overview

A bacterial infection of the kidney itself (as opposed to a lower urinary tract infection confined to the bladder), which can cause both acute illness and, if it becomes chronic or recurrent, progressive kidney damage over time.

Symptoms

• Lethargy (moderate, very common)
• Fever (moderate, common)
• Decreased appetite (moderate, common)
• Back or abdominal pain (moderate, common)

Causes

Most commonly caused by bacteria ascending from a lower urinary tract infection up into the kidney, though bacteria can occasionally reach the kidney via the bloodstream from an infection elsewhere in the body. A bacterial infection of the kidney itself (as opposed to a lower urinary tract infection limited to the bladder), pyelonephritis typically develops from bacteria ascending upward from the bladder, or less commonly from bloodborne spread of infection from elsewhere in the body — genuinely more serious than a simple bladder infection given the kidney's vital ongoing filtering function.

Risk Factors

Pre-existing urinary tract abnormalities, urinary stones providing a surface for bacteria to persist on, diabetes (which increases infection susceptibility generally), and any condition causing urine to sit longer than normal in the urinary tract.

Transmission

Not contagious between animals — this is an individual cat's own bacterial infection, not something transmitted cat-to-cat.

Incubation Period

Variable, typically developing over days from an ascending lower urinary tract infection.

Disease Stages & Progression

Can present acutely with sudden illness, or develop more insidiously if low-grade and initially mild — untreated or inadequately treated infection can become chronic, causing progressive kidney scarring over time.

Early Warning Signs

Lethargy, decreased appetite, and possibly signs of lower urinary tract infection (straining, frequent urination) if that's how the infection ascended.

Advanced Symptoms

Fever, back/abdominal pain (sometimes visible as reluctance to be handled around the flank area), vomiting, and in severe cases signs of sepsis (bacteria spreading into the bloodstream) or acute kidney injury.

Diagnostic Methods

Urine culture is the definitive diagnostic test, ideally from a sample collected via cystocentesis (a needle sample directly from the bladder) to avoid contamination, identifying the specific bacteria and which antibiotics will be effective. Urine culture identifying the specific bacteria present, alongside bloodwork assessing kidney function and inflammatory markers, and often ultrasound imaging to assess the kidney's structure and look for any obstruction or abscess formation, together build a complete diagnostic picture.

Veterinary Examination Process

Fever, pain on abdominal palpation (particularly over the kidney area), and overall assessment of hydration and illness severity.

Recommended Lab Tests

Urinalysis, urine culture and sensitivity testing (essential for choosing an effective antibiotic), and blood work to assess kidney function and infection severity.

Diagnostic Imaging

Abdominal ultrasound can show kidney inflammation/enlargement and help identify any predisposing structural issue like stones.

Blood Test Indicators

Elevated white blood cell count indicating infection/inflammation; kidney values (BUN, creatinine) may be elevated if kidney function is affected.

Biopsy / Histopathology

Not typically needed for diagnosis; the combination of clinical signs, imaging, and urine culture is usually sufficient.

Differential Diagnoses

Lower urinary tract infection without kidney involvement, other causes of kidney inflammation, and other causes of fever/lethargy in a cat.

Home Monitoring Guidance

Not appropriate for a suspected active kidney infection — this needs prompt veterinary diagnosis and antibiotic treatment; delaying risks both worsening illness and permanent kidney damage.

Veterinary Treatment Options

A course of antibiotics selected based on urine culture results, typically longer than for a simple bladder infection given how much harder it is for antibiotics to reach effective concentrations in kidney tissue. IV fluids may be needed for more severely affected cats. A prolonged course of appropriate antibiotics (chosen based on culture and sensitivity results specifically, given how important using an effective, correctly-targeted antibiotic is for a kidney infection) is standard, generally longer than the course used for a simple bladder infection given the kidney tissue involvement; IV fluids and supportive care are often needed for more significantly affected cats, particularly if kidney function is notably impaired at diagnosis.

Surgery Requirements

Not typically needed unless there's an underlying structural problem (like an obstructing stone) that also requires correction.

Recovery Timeline

Typically several weeks of antibiotic treatment, with follow-up urine culture recommended to confirm the infection has genuinely cleared rather than just symptoms improving.

Possible Complications

Chronic kidney damage/scarring if the infection isn't fully treated or recurs repeatedly, and in severe untreated cases, sepsis or acute kidney injury.

Long-Term Management

Addressing any underlying predisposing factor (stones, diabetes management) reduces recurrence risk; a cat with a history of pyelonephritis may benefit from periodic urine monitoring.

Prevention

Prompt, complete treatment of any lower urinary tract infection reduces the chance of it ascending to the kidney; managing predisposing conditions like diabetes and urinary stones also helps.

Vaccination Availability

Not applicable — not a vaccine-preventable condition.

Prognosis

Good with prompt, appropriate antibiotic treatment based on culture results; the prognosis is more guarded with delayed treatment, recurrent infections, or significant kidney damage already present.

References

American Association of Feline Practitioners (AAFP); International Society for Companion Animal Infectious Diseases (ISCAID) guidelines on urinary tract infections.

Medications Used

• Antibiotics, selected based on culture and sensitivity results
• IV fluids for more severe cases
• Pain management if needed

Estimated Treatment Cost by Country

Frequently Asked Questions