What are the diagnostic guidelines for acute pyelonephritis (infection of the kidney)?

From the Guidelines

The diagnosis of acute pyelonephritis should be based on a combination of clinical symptoms, physical examination findings, and laboratory tests, including urinalysis, urine culture, and antimicrobial susceptibility testing, as recommended by the most recent guidelines 1. The diagnostic approach to acute pyelonephritis involves identifying patients with symptoms such as flank pain, fever (>38°C), chills, nausea, vomiting, and costovertebral angle tenderness, often accompanied by lower urinary tract symptoms like dysuria, frequency, and urgency.

• Key diagnostic steps include:
  • Urinalysis to assess for pyuria, bacteriuria, and sometimes hematuria
  • Urine culture and antimicrobial susceptibility testing to guide antibiotic therapy
  • Blood tests to evaluate for elevated white blood cell count and inflammatory markers like C-reactive protein
  • Blood cultures for patients with severe illness, immunocompromise, or those requiring hospitalization
• Imaging is not routinely needed for uncomplicated cases but should be considered for patients with severe illness, those not responding to treatment within 72 hours, recurrent infections, or when complications like abscess or obstruction are suspected, with CT scan with contrast being the preferred imaging modality, though ultrasound may be used initially, especially in pregnant women or those with renal insufficiency 1.
• The choice of empirical antibiotic treatment should be based on local resistance patterns and guidelines, with fluoroquinolones and cephalosporins being recommended for oral empiric treatment of uncomplicated pyelonephritis 1.
• Prompt differentiation between uncomplicated and potentially obstructive pyelonephritis is crucial, as the latter can swiftly progress to urosepsis, and should be established using appropriate imaging techniques 1.

From the Research

Diagnostic Guidelines for Acute Pyelonephritis

The diagnostic guidelines for acute pyelonephritis involve a combination of clinical evaluation, laboratory tests, and imaging studies. The key diagnostic criteria include:

• Fever, flank pain or tenderness, and leukocytosis 2, 3
• Pyuria, which is the presence of pus in the urine 2, 3
• Confirmatory urine culture, which is positive in 90% of patients with acute pyelonephritis 2
• Gram stain of unspun urine, which can provide an early clue regarding the etiologic agent 3

Laboratory Tests

The laboratory tests used to diagnose acute pyelonephritis include:

• Urinalysis, which includes a leukocyte esterase test and a nitrite test 2
• Urine culture, which should be obtained before antibiotic therapy is initiated 2, 4, 5
• Blood cultures, which should be reserved for patients with an uncertain diagnosis, those who are immunocompromised, and those who are suspected of having hematogenous infections 2

Imaging Studies

Imaging studies, such as computed tomography (CT) scans, are not necessary unless there is no improvement in the patient's symptoms or if there is symptom recurrence after initial improvement 4, 5, 6

Classification of Acute Pyelonephritis

Acute pyelonephritis can be classified into two categories:

• Uncomplicated pyelonephritis, which can be managed as outpatients with oral antibiotics 4, 5
• Complicated pyelonephritis, which requires hospitalization, supportive therapies, and administration of wide-spectrum intravenous antibiotic therapy 4