Which imaging modality is often used first to assess obstruction causing AKI?

• A. Ultrasound
• B. CT with contrast
• C. MRI
• D. X-ray

Answer: (A)

When obstruction is suspected as a cause of AKI, you want a fast, safe, and informative test. Ultrasound fits that need perfectly. It can be done at the bedside, has no radiation, and does not require contrast, which is important because contrast can worsen kidney function in AKI. The main thing ultrasound looks for is hydronephrosis—swelling of the kidney due to urine buildup from an obstruction. Seeing hydronephrosis (and signs like bladder distension or a visible obstructing stone) directly supports a postrenal cause and helps guide urgent management, such as decompression.

If ultrasound doesn’t show hydronephrosis but suspicion remains high, a different imaging step can be taken, like a noncontrast CT to look for stones or further evaluation with other modalities, but in the acute setting ultrasound is the go-to first choice. MRI is not typically first-line due to availability and time, and X-ray lacks sensitivity for most obstructive causes.