Kidney Infection Symptoms and Treatment: When to Go to Urgent Care

A kidney infection — medically known as pyelonephritis — is a serious bacterial infection that occurs when bacteria travel up from the bladder into one or both kidneys. Unlike a bladder infection (cystitis), a kidney infection requires prompt treatment to prevent potentially life-threatening complications.

Kidney Infection Symptoms

Kidney infection symptoms overlap with UTI symptoms but include additional, more serious signs:

Symptoms Also Present with UTI

• Burning or pain with urination
• Frequent urge to urinate
• Cloudy or foul-smelling urine
• Blood in urine (hematuria)

Symptoms That Suggest Kidney Involvement

• Flank pain: Pain in the back or side, below the ribcage — the hallmark sign of kidney infection. May be on one or both sides.
• Fever (typically 100–104°F) — Often higher than with a simple bladder infection
• Chills and shaking
• Nausea and vomiting
• Fatigue and general illness
• Tender to touch on the back at the kidney area

If you have UTI symptoms plus fever, flank pain, or nausea/vomiting, you likely have a kidney infection (not just a bladder UTI) and need prompt evaluation.

What Causes Kidney Infections?

Most kidney infections are caused by bacteria (usually E. coli) traveling upward from the urethra → bladder → ureters → kidney. This is called an ascending infection. Risk factors include:

• Recent or untreated bladder UTI
• Female anatomy (shorter urethra)
• Pregnancy (enlarged uterus can block urine flow)
• Diabetes (impaired immune function)
• Kidney stones (blockage allows bacterial growth)
• Urinary tract obstruction (enlarged prostate, tumors)
• Urinary catheter use
• Weakened immune system

How Is a Kidney Infection Diagnosed?

At CityHealth San Leandro, diagnosis includes:

1. Urinalysis: Checks for white blood cells, nitrites, and bacteria in urine — results in minutes
2. Urine culture: Identifies the specific bacteria and antibiotic sensitivity — critical for guiding treatment. Results in 24–72 hours.
3. Blood work: Complete blood count (elevated white blood cells confirm infection), kidney function tests (creatinine, BUN), and blood cultures if sepsis is suspected
4. Physical exam: Checking for costovertebral angle (CVA) tenderness — tapping the back at the kidney level reproduces flank pain in kidney infection

If your symptoms suggest severe infection or complications, referral for CT imaging or ER transfer may be necessary.

Kidney Infection Treatment

Treatment depends on severity:

Mild-to-Moderate Kidney Infection (Oral Antibiotics)

Outpatient treatment with a 7–14 day course of oral antibiotics. Common choices:

• Fluoroquinolones (ciprofloxacin, levofloxacin) — first-line if local resistance rates are low
• TMP-SMX (Bactrim) — if sensitivity is confirmed on culture
• Oral cephalosporins (cephalexin) for pregnant patients or if fluoroquinolones are contraindicated

Most patients improve significantly within 24–48 hours of starting antibiotics. Complete the full course even if you feel better.

Severe Kidney Infection (ER Required)

The following require ER evaluation and likely IV antibiotics or hospitalization:

• High fever (above 103°F) not responding to acetaminophen/ibuprofen
• Severe vomiting preventing oral medications or hydration
• Signs of sepsis (rapid heart rate, low blood pressure, altered consciousness)
• Immunocompromised patients (diabetes, HIV, chemotherapy)
• Pregnant women with high fever
• No improvement after 24–48 hours on oral antibiotics

Preventing Kidney Infections

• Treat bladder UTIs promptly — don’t wait for them to resolve on their own
• Stay well-hydrated — drinking plenty of water helps flush bacteria from the urinary tract
• Urinate after sex
• Wipe front to back (for women) to prevent bacteria from entering the urethra
• If you have recurrent UTIs or kidney infections, discuss with your provider about preventive antibiotics