Diagnostic Approach to Pyelonephritis

Clinical Diagnosis and Laboratory Workup

The American College of Radiology recommends obtaining urinalysis with microscopy and urine culture with susceptibility testing before initiating antibiotics in patients with suspected pyelonephritis, as imaging is not routinely indicated for uncomplicated cases 1, 2
Voiding symptoms, such as dysuria, urgency, and frequency, are common in patients with pyelonephritis, but may be absent in up to 20% of patients 2
Systemic symptoms, including chills and fatigue, are also common in patients with pyelonephritis 2
The presence of pyuria and/or bacteriuria on urinalysis with microscopy has 90-96% sensitivity for diagnosing urinary tract infections 4
Leukocyte esterase has 72-97% sensitivity for urinary tract infections, while nitrite has high specificity but lower sensitivity 5

The Journal of the American College of Radiology recommends contrast-enhanced CT as the imaging study of choice when imaging is indicated, with 90-92% accuracy for detecting parenchymal changes 3, 5
Ultrasound has a limited role in detecting parenchymal abnormalities in acute pyelonephritis, but may be preferred in pregnancy to avoid radiation exposure 3
MRI may be used as an alternative when contrast is contraindicated, but has poor accuracy for detecting small ureteral calculi and reduced ability to detect gas 3
High-risk patient populations, such as those with diabetes mellitus, anatomic urinary tract abnormalities, or immunosuppression, may require earlier imaging 3, 5
The American College of Radiology recommends obtaining imaging in patients who fail to respond to appropriate therapy within 72 hours, as well as in those with suspected complications such as renal or perinephric abscesses 3, 4