Comparison of kidney-ureter-bladder abdominal radiography and computed tomography scout films for identifying renal calculi.

OBJECTIVE: To assess the sensitivity of computed tomography (CT) scout topograms and kidney-ureter-bladder abdominal radiography (KUB) in detecting urinary tract stones.

PATIENTS AND METHODS: We assessed films taken on presentation for 163 consecutive patients referred to our service for stone follow-up. Only those with both CT and KUB imaging on the same day were studied further. Two urology registrars examined the films independently. Location, size and length of stone were recorded. Where there was discordance, the films were examined by an independent radiologist.

RESULTS: In all, 108 of 163 patients had both CT and KUB imaging on the same day. Stones were identified in 63% (68/108) of patients with KUB, with a mean length of 4.93 mm. There were 40/108 radiolucent stones subsequently measured on CT, with a mean length of 4.90 mm. Stones were seen on 47% (51/108) of the CT scouts, with a mean length of 5.22 mm. Importantly, all stones visible on CT scout were also visible on KUB. There was no correlation between stone location and visibility on KUB or CT scout films.

CONCLUSION: KUB could be used for follow-up in 63% of cases. All stones seen on CT scout were also visible on KUB. Scout detected 75% of stones visible on KUB. We suggest CT scout film should be reported before proceeding to KUB. If the stone is visible on CT scout film, then the decision to use KUB for follow-up can be made. This minimizes radiation exposure and other costs.