From the Guidelines
To identify pyelonephritis versus a lower urinary tract infection (UTI) in a urine sample, look for specific markers that indicate kidney involvement, such as higher white blood cell counts, white blood cell casts, and renal tubular epithelial cells, as recommended by the European Association of Urology guidelines 1. When differentiating between pyelonephritis and a lower UTI, it is essential to consider the clinical presentation, as pyelonephritis typically presents with fever, flank pain, and systemic symptoms alongside urinary symptoms, while lower UTIs primarily cause dysuria, frequency, and urgency without systemic involvement. Some key points to consider in the diagnosis of pyelonephritis include:
- Urinalysis showing positive nitrites, leukocyte esterase, and bacteria, with higher white blood cell counts (often >20-50 WBCs/hpf) and white blood cell casts, which are highly specific for kidney infection 1.
- Renal tubular epithelial cells in the urine, which also suggest pyelonephritis 1.
- Urine culture showing higher bacterial colony counts (>100,000 CFU/mL) in pyelonephritis 1.
- Elevated inflammatory markers in blood tests, such as elevated WBC, CRP, and procalcitonin, which accompany the urine findings in pyelonephritis 1. It is crucial to note that urine findings alone cannot definitively distinguish between pyelonephritis and lower UTIs, and clinical correlation is always necessary for accurate diagnosis and appropriate treatment, as emphasized by the American College of Radiology 1.
From the Research
Identifying Pyelonephritis vs UTI in a Urine Sample
To differentiate between pyelonephritis and UTI in a urine sample, several factors and tests can be considered:
- Urine Culture: Urine culture with antimicrobial susceptibility testing should be performed in all patients suspected of having pyelonephritis, as it helps direct therapy 2.
- Symptoms: Patients with pyelonephritis typically present with costovertebral tenderness, fever, and urinary symptoms, whereas cystitis symptoms include lower abdominal pain, dysuria, and urinary urgency or frequency 3.
- Urinalysis: Urinalysis can provide valuable information, including the presence of pyuria (white blood cells in the urine), which is a key indicator of infection. A hemocytometer value of ≥ 10 WBC/mm3 or manual microscopy showing ≥ 8 WBC/high-power field can indicate bacteriuria requiring therapy 4.
- Nitrites and Leukocyte Esterase: A positive result for nitrites and leukocyte esterase by urine dipstick can indicate a urinary tract infection, but this may not be sufficient to distinguish between pyelonephritis and UTI 4.
- Imaging and Blood Cultures: In uncomplicated cases, imaging, blood cultures, and measurement of serum inflammatory markers are not necessary. However, in complicated cases or when the patient does not respond to treatment, these tests may be considered 2.
Key Differences
The key differences between pyelonephritis and UTI lie in their symptoms, severity, and treatment approaches:
- Treatment Duration: The duration of treatment varies, ranging from 3 to 5 days for uncomplicated cystitis to 7 to 14 days for pyelonephritis 5.
- Antibiotic Choice: The choice of antibiotics also differs, with third-generation cephalosporins preferred for pyelonephritis and other options like nitrofurantoin, trimethoprim-sulfamethoxazole, and fosfomycin for UTI 3, 2.
- Complications: Pyelonephritis can lead to more severe complications, such as sepsis, septic shock, and kidney damage, especially in pregnant patients, who should be admitted and treated initially with parenteral therapy 3, 2.