Nephrology

Acute Pyelonephritis — Clinical Reference

Last reviewed 2026-06-19 · TruelyserMD Clinical Reference
For Patients & General Readers

Acute pyelonephritis is a serious infection of the kidneys, often starting as a lower urinary tract infection that travels upwards. It commonly affects women and can cause severe flank pain, fever, and nausea. Prompt diagnosis and treatment are crucial to prevent kidney damage and serious complications like sepsis.

Clinical Overview

Acute pyelonephritis is an ascending bacterial infection of the renal parenchyma and pelvis, typically caused by gram-negative bacilli, most commonly E. coli. It presents as a febrile urinary tract infection and can lead to renal abscess, sepsis, and chronic kidney disease if inadequately treated.

Clinical Presentation

Signs & Symptoms

Symptoms (Patient-Reported)

  • Sudden onset of fever
  • Pain in the side and back (flank pain)
  • Feeling sick to your stomach (nausea)
  • Throwing up (vomiting)
  • Pain or burning when you urinate
  • Needing to urinate more often than usual

Signs (Clinician-Observed)

  • Fever
  • Costovertebral angle tenderness
  • Tachycardia
  • Hypotension (in severe cases)

Differential Diagnoses

ConditionDistinguishing Feature
Acute CholecystitisRight upper quadrant pain, often associated with meals, positive Murphy's sign, and elevated liver enzymes.
Nephrolithiasis (Kidney Stones)Colicky flank pain radiating to the groin, hematuria, and often absence of fever unless complicated by infection.
AppendicitisPeriumbilical pain migrating to the right lower quadrant, anorexia, and rebound tenderness.
PneumoniaPulmonary symptoms (cough, dyspnea, pleuritic chest pain), and abnormal lung auscultation findings.
Musculoskeletal PainPain localized to the back or flank without systemic signs of infection or urinary symptoms, often reproducible with palpation of muscles or spine.
Pelvic Inflammatory Disease (PID)Lower abdominal pain, vaginal discharge, cervical motion tenderness, and fever, typically in sexually active women.

Red Flags — Seek Immediate Care

Key Investigations

Management Overview

Management involves prompt initiation of empirical antibiotic therapy targeting common uropathogens, with adjustments based on urine culture results. Hospitalization is indicated for patients with severe symptoms, signs of sepsis, inability to tolerate oral intake, or underlying risk factors. Adequate hydration and pain management are crucial supportive measures.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. TruelyserMD does not replace clinical judgement.