What is the initial workup for a patient presenting with possible kidney stone symptoms?

Initial Workup for Suspected Kidney Stones

Non-contrast CT scan of the abdomen and pelvis is the gold standard for initial evaluation of suspected kidney stones, with sensitivity up to 97% for detecting urolithiasis and other causes of flank pain. 1

Initial Diagnostic Approach

First-Line Imaging Options:

• Non-contrast CT of abdomen and pelvis:

  • Gold standard with highest diagnostic accuracy (sensitivity up to 97%) 1
  • Provides precise information about stone size, location, and density 1, 2
  • Particularly useful when moderate to severe hydronephrosis is present on ultrasound, as these patients have higher risk of stone passage failure 2
  • Can identify alternative diagnoses in patients with flank pain 2

• Ultrasound (alternative first-line option):

  • Recommended to limit radiation exposure, especially in younger patients, pregnant women 1
  • High sensitivity for detecting large stones (>5mm), but accuracy decreases significantly for stones <3mm 3
  • Any degree of hydronephrosis on ultrasound makes the presence of a ureteral stone on subsequent CT more likely (PPV 88%) 2
  • Less sensitive than CT for detecting ureteric stones (sensitivity of 45% for ultrasound alone) 4

Clinical Assessment:

• Evaluate for classic symptoms of renal colic: severe flank pain radiating to the groin, often associated with hematuria 5
• Approximately 90% of stones that cause renal colic pass spontaneously 5, 6
• Instruct patients to strain urine to recover stone for analysis 5

Imaging Algorithm Based on Clinical Presentation

For typical renal colic symptoms:

1. Non-contrast CT abdomen and pelvis is preferred first-line imaging 1, 2

   • Consider low-dose CT protocols (<3 mSv) which maintain high diagnostic accuracy (sensitivity 97%, specificity 95%) 3
   • CT can identify alternative diagnoses in 13% of patients with flank pain, with 7% requiring additional management 2

2. Ultrasound + KUB X-ray as alternative approach:

   • Combined ultrasound and KUB improves sensitivity for urolithiasis compared to either modality alone 2
   • Ultrasound has high sensitivity and specificity for hydronephrosis (93% and 100% respectively) 4
   • KUB X-ray can detect radiopaque stones (90% of stones are radio-opaque) 2
   • Combined approach reduces radiation exposure 3

Special Considerations

• High-grade obstruction or failure of oral analgesics to relieve pain may require hospitalization 5
• Urinary tract infection with obstruction is a urologic emergency requiring immediate drainage, usually with a ureteral stent 5
• For improved visualization of the collecting system during CT, consider oral hydration (1L water) and oral diuretic (20mg furosemide) 30-60 minutes before the scan 7

Common Pitfalls and Caveats

• Contrast-enhanced CT may obscure stones within the renal collecting system 1
• Delayed development of secondary signs of obstruction may lead to false-negative ultrasound findings 1
• Lack of hydronephrosis does not rule out kidney stones (NPV 65%) 2
• Ultrasound has lower sensitivity for ureteric stones compared to renal stones 4

Follow-up Imaging

• Repeat imaging is indicated when symptoms change or if stone passage is suspected but needs confirmation 3
• If medical expulsive therapy is not successful after 4-6 weeks, imaging should be performed before offering definitive treatment 3