Diagnostic Approach to Male Patients with Flank Pain and Low-Grade Fever

Initial Evaluation

Non-contrast CT of the abdomen and pelvis is the best initial test for detecting urinary stones and identifying alternative diagnoses, with 98-100% sensitivity and specificity, as recommended by the American College of Radiology 1, 2
The combination of flank pain and low-grade fever creates a diagnostic challenge that requires imaging capable of detecting both obstructive urolithiasis and infectious/inflammatory complications, with non-contrast CT achieving 98-100% sensitivity and specificity for urinary stones of any size, location, or composition 1, 2, 3

Non-contrast CT identifies alternative diagnoses in approximately one-third of patients presenting with flank pain, including infectious complications like pyelonephritis or perinephric abscess 2
The presence of fever shifts the differential diagnosis toward infectious etiologies, which can be visualized on non-contrast CT, with fever being nearly universal in acute pyelonephritis 3
Pain that worsens significantly with external flank pressure suggests infection rather than uncomplicated stone disease, as noted by the American College of Radiology 1, 3

Contrast-enhanced CT may be more appropriate if infectious etiology is strongly suspected, but it may obscure stones within the renal collecting system if stone disease is the primary concern, according to the American College of Radiology 3, 4
Low-dose CT protocols are non-inferior to standard-dose for detecting ureteral stones with 92-99% sensitivity, as recommended by the Journal of the American College of Radiology 4

The American College of Radiology recommends considering contrast-enhanced imaging if there is strong clinical suspicion for complicated infection, initial non-contrast CT is inconclusive, or no improvement in symptoms after initial management 3, 4
Hemodynamic instability, inability to urinate, or decreased urine output requires urgent evaluation, as noted by the American College of Radiology 2
Signs of systemic infection suggest complicated pyelonephritis or sepsis, requiring immediate attention, according to the American College of Radiology 2