🦠 Vet Guide 2025: Pyelonephritis in Dogs and Cats – Kidney Infections, Diagnosis & Treatment 🐶🐱🩺

By Dr Duncan Houston, BVSc

💡 What Is Pyelonephritis?

Pyelonephritis, also called pyelitis or upper urinary tract infection, is a bacterial infection that affects the kidneys' internal structures, including the renal pelvis and parenchyma. This condition is often silent until it becomes severe and can lead to kidney damage or failure if untreated. 🦠💧

📈 How Common Is It?

Pyelonephritis is relatively common—especially in older pets. Many cases go undiagnosed until testing reveals damage or until the infection becomes life-threatening.

🧪 What Causes Pyelonephritis?

The infection usually ascends from the bladder through the ureters, but it can also spread through the bloodstream from other infections, including:

• 🦷 Dental disease
• 🦴 Diskospondylitis
• ❤️ Bacterial endocarditis
• 💥 Internal abscesses

Pets with bladder stones, urethral obstruction, kidney trauma, urinary stasis, or suppressed immunity are at higher risk. 🐶🐱

🧬 Clinical Signs (Often Subtle)

Unfortunately, many pets with pyelonephritis show no signs until late. When symptoms appear, they may include:

• 🌡️ Fever
• 💦 Increased thirst (polydipsia)
• 🚽 Frequent urination (polyuria)
• 🛏️ Lethargy
• 🤢 Nausea or vomiting
• 🩸 Blood in urine

Because these signs overlap with many conditions (like CKD, UTI, and diabetes), a full diagnostic workup is critical.

🧪 Diagnosis

Your veterinarian will likely recommend:

• 🧫 Urinalysis: To detect low specific gravity, blood, white cells, or bacteria
• 🧪 Urine culture: To identify bacteria and test for antibiotic sensitivity
• 🧬 Blood tests: CBC and chemistry panel to check kidney markers and inflammation
• 🖥️ Ultrasound or X-rays: To check kidney shape, size, stones, or abnormalities

Why Specific Gravity Matters

The kidneys concentrate urine. Low urine concentration (specific gravity) in combination with infection suggests kidney involvement.

💊 Treatment

• 💉 Long-term antibiotics (4–6 weeks or more)
• 🔬 Choice of antibiotics is based on culture and sensitivity testing
• 📆 Re-check urinalysis and culture 5–7 days after starting treatment
• 🧪 Repeat tests again 1 week post-treatment and at 1, 3, and 6 months

📋 Monitoring

• 🩺 Monitor specific gravity regularly (decreasing SG may signal recurrence)
• 📸 Periodic imaging for structural issues or stones

📉 Prognosis

Pyelonephritis generally has a fair to good prognosis with early diagnosis and appropriate treatment. However, prognosis worsens in pets with:

• 🧬 Pre-existing kidney disease
• 🪨 Kidney stones (nephroliths)
• 🎗️ Cancer (e.g., kidney or bladder tumors)
• 🩺 Endocrine disorders like Cushing’s or diabetes

⚠️ Why Early Detection Matters

Because pyelonephritis is often asymptomatic early on, it’s important to investigate subtle changes in thirst, urination, or urine concentration. Delayed diagnosis can result in irreversible kidney damage or chronic renal failure. 🧪

🩺 Final Thoughts from Dr Duncan Houston

Pyelonephritis may not announce itself loudly—but its effects on the kidneys can be profound. Catching this infection early and following through with long-term antibiotic therapy and rechecks can save your pet’s kidney function. When in doubt, test. Trust your instincts and follow up if you notice any changes in your pet’s urination or behavior. 🐾🦠

📲 Worried About a Urinary Tract Infection? Ask A Vet Now

If you suspect pyelonephritis or a kidney infection, don’t delay. Get expert help through the Ask A Vet app. Chat live with Dr Duncan Houston and licensed professionals for advice, diagnostics, or second opinions 🐶🐱💬