An infant with a history of ureteropelvic junction (UPJ) obstruction has serial ultrasounds showing an increase in anteroposterior (AP) renal pelvic diameter from 12 mm to 25 mm over 3 months. Which study is indicated to assess functional drainage?
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✓ Correct answer: C. Diuretic renogramThe correct answer is a diuretic renogram (e.g., MAG-3 scan). Worsening hydronephrosis (increasing AP diameter) requires functional assessment to determine if obstruction is significant enough to damage renal function. The renogram measures split function and drainage time. Distractor 1 is a reflux study, not primarily for obstruction. Distractor 2 exposes the child to high radiation and is not first-line for functional assessment. Distractor 3 is incorrect as the worsening trend mandates evaluation, not just observation. Distractor 4 is invasive and premature.
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