Which imaging modality is preferred for initial evaluation of suspected nephrolithiasis in a nonpregnant adult?

• A. Non-contrast CT abdomen/pelvis.
• B. Ultrasound abdomen.
• C. KUB radiograph.
• D. MRI pelvis.

Answer: (D)

For a nonpregnant adult with suspected kidney stones, non-contrast CT of the abdomen/pelvis is the preferred initial imaging because it detects stones of all sizes and compositions with high accuracy, and it rapidly shows whether there is obstruction, hydronephrosis, or other causes of pain. CT provides a comprehensive view and guides urgent management, unlike other modalities that have more limited sensitivity. Ultrasound can be used when radiation should be avoided or in specific populations (like pregnancy or children), but it is less sensitive for detecting small stones. KUB radiographs miss a substantial portion of stones, especially radiolucent ones, and MRI is not effective for visualizing calcified stones. Therefore, non-contrast CT is the best first test for suspected nephrolithiasis in a nonpregnant adult.