What diagnostics are recommended in the ER for evaluation of kidney stones?

Diagnostic Evaluation of Kidney Stones in the Emergency Room

Non-contrast CT scan is the first-line diagnostic test for suspected kidney stones in the emergency room due to its high sensitivity and specificity exceeding 95%. 1

Primary Imaging Modalities

Non-Contrast CT Scan

• Gold standard for kidney stone diagnosis with sensitivity and specificity >95% 2
• Provides precise information about:
  • Stone size (critical for treatment planning)
  • Stone location (helps predict likelihood of spontaneous passage)
  • Degree of obstruction
• Low-dose CT protocol should be used instead of conventional dosing to reduce radiation exposure 1
• Allows for identification of alternative diagnoses in 10-15% of patients presenting with flank pain 3

Ultrasound

• Appropriate alternative in specific situations:
  • First-line imaging for pregnant patients 1, 2
  • Patients requiring repeated imaging to reduce cumulative radiation exposure
  • Children with suspected kidney stones
• Limitations:
  • Lower sensitivity (45%) and specificity (88%) compared to CT 2
  • Poor detection of small stones (<3mm) 1
  • Operator-dependent results

Clinical Decision Algorithm

1. For non-pregnant adults with first presentation of suspected kidney stones:

   • Proceed directly to low-dose non-contrast CT of abdomen and pelvis 1
   • This provides the most accurate diagnosis and guides treatment decisions

2. For pregnant patients:

   • Ultrasound is the imaging modality of choice 1, 2
   • MRI can be considered as a second-line option if ultrasound is inconclusive

3. For patients with recurrent stone disease:

   • Consider starting with ultrasound if prior imaging confirmed stones 1
   • If symptoms persist or worsen, proceed to low-dose CT

Important Considerations

• Size and location matter: Stones <5mm in the proximal ureter are likely to pass spontaneously, while larger stones may require intervention 1

• Radiation concerns: Standard CT delivers higher radiation dose than other imaging tests, making low-dose protocols essential 1, 4

  • Low-dose CT can detect stones >3mm with sensitivity of 87% and specificity of 100% 4

• Alternative diagnoses: In patients without history of urolithiasis and negative urinalysis, consider contrast-enhanced CT as up to 15% may have alternative diagnoses 3

• Abdominal radiography (KUB): Not recommended as initial imaging due to limited sensitivity (~49%) 2

  • May be useful for monitoring known stone disease but not for initial diagnosis 1

Common Pitfalls to Avoid

1. Relying solely on urinalysis - while microscopic hematuria is common with kidney stones, its absence doesn't exclude the diagnosis 5

2. Using contrast-enhanced CT as initial imaging - contrast can obscure stones 3

3. Failing to consider alternative diagnoses in patients with negative imaging but persistent symptoms

4. Not using low-dose CT protocols, unnecessarily increasing radiation exposure 1, 4

By following this evidence-based approach to imaging, clinicians can accurately diagnose kidney stones while minimizing radiation exposure and identifying alternative diagnoses when present.