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Pyelonephritis

Pyelonephritis is a bacterial infection of the renal pelvis and kidney parenchyma, usually caused by an ascending urinary tract infection. It commonly presents with fever, flank pain, and urinary symptoms and can progress to sepsis if severe

Also called

Kidney infection

ICD-10

N10 + N11.9

Specialty

Nephrology

Onset

Acute & Chronic

Reviewed

August 2026
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Overview

-Pyelonephritis may be:

  • Acute: sudden bacterial infection causing inflammation of the kidney
  • Chronic/recurrent: repeated infection or associated urinary abnormalities causing renal scarring

-Common causative organisms include:

  • Escherichia coli (E. coli) — most common
  • Klebsiella species
  • Proteus species
  • Other Enterobacterales

Etiology & Risk Factors

-Etiology

–Usually results from an ascending bacterial infection from the lower urinary tract.

-Less commonly, infection reaches the kidney through hematogenous spread

 

-Risk Factors:

  • Female sex
  • Urinary tract obstruction
  • Kidney stones
  • Vesicoureteral reflux
  • Diabetes mellitus
  • Pregnancy
  • Urinary catheterization
  • Structural urinary tract abnormalities

Pathophysiology

Lower urinary tract bacterial infection → ascending bacterial spread → renal pelvis and parenchymal infection → interstitial inflammation → renal tissue injury → systemic inflammatory response

Clinical Presentation

-Symptoms:

  • Fever
  • Chills or rigors
  • Flank pain
  • Dysuria
  • Urinary frequency
  • Urinary urgency
  • Nausea and vomiting
  • Malaise

-Signs:

  • Fever
  • Tachycardia
  • Costovertebral angle tenderness
  • Flank or abdominal tenderness
  • Dehydration
Pyelonephritis Overview
Pyelonephritis Overview

History Taking

-Ask about:

  • Fever and chills
  • Flank or back pain
  • Dysuria
  • Urinary frequency and urgency
  • Hematuria
  • Nausea and vomiting
  • Previous urinary tract infections
  • Kidney stones
  • Urinary obstruction
  • Recent urinary procedures
  • Pregnancy
  • Diabetes mellitus

Physical Examination

-General Examination

  • Temperature
  • Heart rate
  • Blood pressure
  • Hydration status
  • Signs of sepsis

 

-System-Specific Examination:

  • Costovertebral angle tenderness
  • Flank tenderness
  • Suprapubic tenderness
  • Abdominal examination for obstruction or complications

Investigations

-Biochemistry / Specific Tests

  • Urinalysis

  • Urine culture and antimicrobial susceptibility testing

  • Serum creatinine and eGFR when systemic illness, complicated infection, or kidney dysfunction is suspected

  • Serum electrolytes when clinically indicated

  • Blood cultures in severe infection or sepsis

Typical urine findings include:

  • Pyuria

  • Bacteriuria

  • Positive leukocyte esterase

  • Possible hematuria

  • White blood cell casts may occur

 

Imaging

Imaging is not routinely required in uncomplicated Pyelonephritis.

Consider renal ultrasound or CT when there is:

  • Suspected urinary obstruction

  • Kidney stones

  • Severe or complicated infection

  • Persistent fever despite treatment

  • Recurrent infection

  • Suspected renal or perinephric abscess

 

-Special / Confirmatory Tests

Urine culture is the key microbiological investigation and should be obtained before antibiotics when feasible, particularly in complicated disease

Diagnosis

–Diagnosis of Pyelonephritis is usually clinical, supported by:

  • Fever or systemic symptoms
  • Flank pain
  • Costovertebral angle tenderness
  • Urinary symptoms
  • Pyuria and bacteriuria

Urine culture confirms the causative organism and provides antimicrobial susceptibility information.

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Management

1. First-Line / Emergency Management

For severe infection or sepsis:

  • Assess and stabilize airway, breathing, and circulation

  • Obtain cultures when feasible without delaying antibiotics

  • Start appropriate IV antibiotics promptly

  • IV fluids for sepsis or significant volume depletion

  • Manage septic shock according to standard protocols

Infected urinary obstruction → urgent urological drainage.

 

2. Definitive Treatment

  • Appropriate antibiotic therapy

  • Treat urinary obstruction or structural abnormalities

  • Remove or replace infected urinary devices when appropriate

 

3. Medical Treatment

Antibiotic choice depends on local resistance patterns, severity, previous cultures, and patient factors.

Common options include:

  • Fluoroquinolones in appropriate patients and settings

  • Third-generation cephalosporins

  • Trimethoprim–sulfamethoxazole when the organism is susceptible

  • Other antibiotics guided by culture and susceptibility results

Stable uncomplicated cases may be treated with appropriate oral therapy, while severe or complicated infection generally requires initial IV therapy.

 

4. Surgical / Procedural Treatment

Procedures are required when there is infected obstruction or an abscess:

  • Ureteric stent

  • Percutaneous nephrostomy

  • Drainage of renal or perinephric abscess when indicated

 

5. Supportive Management

  • Adequate hydration

  • Antipyretics and analgesia

  • Monitor urine output

  • Monitor kidney function in complicated disease

Complications

  • Sepsis
  • Septic shock
  • Acute Kidney Injury (AKI)
  • Renal abscess
  • Perinephric abscess
  • Papillary necrosis
  • Renal scarring
  • Recurrent urinary tract infection
  • Chronic Pyelonephritis
  • Chronic Kidney Disease (CKD)

Prognosis

-Most patients with uncomplicated acute Pyelonephritis recover completely with appropriate antibiotic treatment.

-Prognosis is worse with urinary obstruction, resistant organisms, delayed treatment, diabetes, or severe sepsis. Recurrent or chronic infection can cause renal scarring and progressive Chronic Kidney Disease (CKD).

Key Points / Clinical Pearls

  • Pyelonephritis is a bacterial infection of the renal pelvis and kidney parenchyma.
  • Most cases result from an ascending urinary tract infection.
  • Escherichia coli (E. coli) is the most common causative organism.
  • Fever, flank pain, and costovertebral angle tenderness are classic findings.
  • Dysuria, frequency, and urgency may accompany upper urinary tract infection.
  • Pyuria and bacteriuria are common.
  • Urine culture is the key microbiological investigation.
  • Blood cultures are indicated in severe infection or sepsis.
  • Imaging is not routinely required in uncomplicated cases.
  • Imaging is important when obstruction, stones, abscess, or treatment failure is suspected.
  • Antibiotics are the mainstay of treatment.
  • Severe or complicated infections may require IV antibiotics.