How to diagnose kidney stones?

Diagnosing Kidney Stones

Non-contrast CT of the abdomen and pelvis is the gold standard for diagnosing kidney stones with a sensitivity of up to 97% and should be the first-line imaging modality when kidney stones are suspected. 1

Diagnostic Algorithm for Suspected Kidney Stones

First-Line Imaging

• Non-contrast CT abdomen and pelvis
  • Highest sensitivity (97%) for detecting urolithiasis 1
  • Can detect virtually all renal calculi without IV contrast
  • Provides accurate stone size and location measurements
  • Visualizes secondary signs of obstruction (hydronephrosis, perinephric inflammation)
  • Low-dose protocols (<3 mSv) maintain 97% sensitivity while reducing radiation exposure 1

Alternative First-Line Options (Special Situations)

• Ultrasound (US) of kidneys and bladder
  • Preferred for pregnant patients 1
  • Appropriate for pediatric patients
  • Useful for patients requiring frequent monitoring
  • Limitations: lower sensitivity (54%) compared to CT 2
  • Can detect hydronephrosis but may overestimate stone size in the 0-10mm range 2

Second-Line or Complementary Imaging

• KUB (Kidney, Ureter, Bladder) X-ray
  • Limited sensitivity (53-62%) for stone detection 1
  • Most useful for follow-up of known radio-opaque stones
  • Not recommended as standalone first-line test 1
  • May complement ultrasound to improve overall sensitivity 1

Clinical Considerations

Stone Size and Management Implications

• CT provides the most accurate stone measurements, critical for treatment decisions:
  • Stones <5mm: typically managed conservatively
  • Stones ≥5mm: may require intervention
  • Ultrasound overestimates stone size in the 0-10mm range, potentially leading to inappropriate management in 22% of cases 2

Special Populations

• Pregnant patients:

  • Ultrasound is first-line (appropriateness rating 8/9) 1
  • Low-dose non-contrast CT may be considered in second/third trimesters if ultrasound is inconclusive 1

• Recurrent stone formers:

  • Low-dose non-contrast CT (appropriateness rating 7/9) 1
  • Ultrasound may be appropriate for monitoring (appropriateness rating 7/9) 1

Pitfalls to Avoid

1. Relying solely on ultrasound for treatment decisions

   • May lead to inappropriate management in approximately 1 in 5 patients 2
   • Particularly problematic for stones in the 5-10mm range, where 43% of patients might receive inappropriate recommendations 2

2. Misinterpreting CT findings

   • Motion artifacts can cause stones to appear larger than actual size 3
   • Consider correlation with KUB or ultrasound when CT findings seem discordant with clinical presentation

3. Using contrast-enhanced CT as first-line

   • Enhancing renal parenchyma may obscure stones within the collecting system 1
   • If contrast-enhanced CT has already been performed, it remains highly accurate (98%) for stones ≥6mm 1

Conclusion of Diagnostic Workup

When kidney stones are suspected, non-contrast CT abdomen and pelvis provides the most accurate diagnosis and should be the first imaging choice for most patients, with ultrasound reserved for pregnant patients, children, and those requiring frequent monitoring.