Does a baseline KUB help facilitate stone management in patients presenting to the emergency department with renal colic?

OBJECTIVES: A baseline KUB (kidney-ureter-bladder) radiograph, at the time of Computed Tomography (CT) for ureteral stones, might aid interpretation of future KUBs. However, the CT's scout radiograph might render the baseline KUB redundant. We sought to assess the diagnostic utility of baseline KUB for patients with ureteral stones.

METHODS: Patients with ureteral stones were retrospectively identified. All had a baseline KUB in addition to CT, and were reassessed after 4-60 days with KUB. Each patient's imaging was randomized 1:1 into either "KUB&CT" or "CT" groups. Three urologists independently assessed the imaging: CT (with scout) and baseline KUB in the "KUB&CT" group, but only the CT (not KUB) in the "CT" group. Definitive stone assessment on follow-up KUB was defined as all 3 reviewers answering either Yes or No (not Indeterminate) to the question of stone passage or migration.

RESULTS: Of 154 stones, the mean diameter was 4.8±2.1mm, density was 914±300HU, with 54.4% in the distal ureter. Stone visibility was 60.4% on KUB vs. 43.5% on scout (p<0.001). Scout visibility favoured the CT group (52.7 vs. 35.0%, p=0.027). After adjusting for BMI, skin-to-stone distance (SSD), size, density and location, definitive assessment rates were higher in the KUB&CT group (p=0.047). When reviewers reassessed the CT group using the baseline KUB, they were able to do so definitively in an additional 16 (21.6%, p<0.001). Definitive assessments were associated with higher rates of stone visibility on scout (86.1 vs. 21.1%, p<0.001), KUB (86.1 vs. 50.0%, p<0.001), and larger (6.0 vs. 3.7 mm, p<0.001), denser stones (1046 vs. 802 HU, p<0.001).

CONCLUSIONS: The addition of a baseline KUB to the CT scout film improves the ability of urologists to determine stone outcome when following patients with KUB imaging, and might reduce the subsequent need for additional imaging.