What is the gold-standard initial imaging for suspected nephrolithiasis in adults?

• A. Ultrasound of the kidneys and bladder
• B. Non-contrast CT abdomen/pelvis
• C. X-ray KUB
• D. MRI abdomen

Answer: (B)

Non-contrast CT of the abdomen and pelvis is the imaging test of choice when nephrolithiasis is suspected in adults because it has the highest sensitivity and specificity for detecting stones of all sizes and compositions. It precisely localizes the stone’s location, determines whether there is obstruction or hydronephrosis, and can reveal other conditions that might mimic renal colic. Because it uses no contrast, it avoids potential risks to the kidneys and contrast reactions, which is important in the acute setting.

Ultrasound can be useful when radiation exposure is a concern or in specific populations, but it is less reliable for detecting ureteral stones, especially in certain locations and in patients with higher body mass index. A plain X-ray of the kidneys, ureters, and bladder misses many stones (including radiolucent ones) and doesn’t reliably assess obstruction. MRI isn’t used for acute stone evaluation because stones are not well visualized on MRI and CT provides a faster, more accurate assessment.