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Infectious Disease

Acute Pyelonephritis

Bacterial infection of the renal parenchyma and collecting system; presents with fever, flank pain and pyuria on top of lower UTI symptoms.

Last reviewed 17 Jul 2026 - MedicoMedics editorial team

Kidney with pyelonephritis inflammation

Pathophysiology

Ascending E. coli infection (~80%); Klebsiella, Proteus, Enterococcus in complicated cases. Risk: obstruction, VUR, pregnancy, diabetes.

Sources: IDSA UTI 2010; ACOG Pyelonephritis in Pregnancy

Presentation

Fever, chills, flank pain, costovertebral angle tenderness plus dysuria/urgency; nausea and vomiting may impair oral therapy.

Diagnosis

Urinalysis (WBC casts diagnostic of upper tract), urine culture, blood culture in severe or hospitalised patients. Imaging (CT or renal US) if no improvement in 72 h or obstruction suspected.

Management

Outpatient: oral fluoroquinolone or IV ceftriaxone loading dose then oral. Inpatient: ceftriaxone or piperacillin-tazobactam; adjust to culture. Duration 7-14 days.

Sample USMLE-style MCQs

Try 5 questions on this topic. Practice hundreds more free with a trial.

Question 1

30-year-old woman with fever, flank pain, dysuria, WBC casts. Best empiric outpatient therapy?

Question 2

Pregnant patient with pyelonephritis at 24 weeks. Best therapy?

Question 3

Diabetic with pyelonephritis and gas on CT. Diagnosis?

Question 4

Which imaging is best for suspected obstruction?

Question 5

Complication of untreated pyelonephritis?

References

Primary guidelines and peer-reviewed sources used for this entry. Reviewed 17 Jul 2026 by MedicoMedics editorial team.

  1. IDSA UTI 2010
  2. ACOG Pyelonephritis in Pregnancy

Frequently asked

Which finding on urinalysis suggests upper tract?

WBC casts.

When to image?

No improvement in 48-72 h, sepsis, obstruction, prior stones.

Emphysematous pyelonephritis?

Gas-forming infection in diabetics - emergency drainage.

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