• Clinical science



Pyelonephritis is an infection of the renal pelvis and parenchyma that is usually associated with an ascending bacterial infection of the bladder. It occurs more commonly in females and risk factors include pregnancy and urinary tract obstruction. Patients typically present with flank pain, costovertebral angle tenderness, fever, and other features of cystitis (e.g., dysuria, frequency). Urinalysis reveals leukocyturia and bacteriuria. Urine cultures should be taken in all patients before initiating treatment to identify the pathogen and possible antibiotic resistance. Treatment depends on the drug sensitivities of the offending pathogen and the patient's clinical profile (e.g., possible comorbidities). Early empiric antibiotic treatment is essential to avoid renal complications and urosepsis.



Clinical features

  • High fever, chills
  • Flank pain, costovertebral angle tenderness (usually unilateral, may be bilateral)
  • Dysuria as well as other symptoms of cystitis (e.g., frequency, urgency)
  • Weakness, nausea, vomiting (diarrhea may also be present)
  • Possible abdominal or pelvic pain



  • Laboratory tests
    • Urinalysis
    • Blood
      • ↑ Inflammatory markers
      • Normal or ↑ renal function parameters
    • Urine culture and blood culture

Urine and blood cultures need to be done before empiric administration of antibiotics!



  • Destructive interstitial nephritis
    • Purulent inflammation of the interstitium with destruction of the parenchyma, the renal tubules, and in some cases the renal pelvis
    • Renal tubules infiltrated with neutrophils
  • Chronic pyelonephritis
    • Chronic inflammatory changes such as rough scarring at the junction of the cortex and medulla
    • Blunted calyces from recurrent urinary reflux
    • Eosinophilic casts in the tubules (so called “thyroidization of the kidney”)
  • Xanthogranulomatous pyelonephritis
    • Lipid laden foamy macrophages and multinucleated giant cells seen on histology
    • Large, irregular, yellow masses appear throughout the kidney on gross examination

Differential diagnoses

The differential diagnoses listed here are not exhaustive.


The choice of treatment and antibiotic therapy should be adjusted according to the Gram stain and drug sensitivities of the identified pathogen, comorbidities, and the current condition of the patient.

Uncomplicated pyelonephritis

Complicated pyelonephritis

In contrast to antibiotic treatment with most cephalosporins, empiric therapy with ciprofloxacin also covers infections with enterococci.



We list the most important complications. The selection is not exhaustive.

Special patient groups

Pyelonephritis in pregnancy

Do not use fluoroquinolones or trimethoprim-sulfamethoxazole in pregnant women!

Chronic pyelonephritis