An inconvenient truth: our routine imaging pathway for loin pain resulted in superfluous radiation exposure

Abstract

Objective: To determine the accuracy of planar radiography of kidney, ureters and bladder (KUB) in detection of urolithiasis when employed as the first-line investigation for loin pain. To put forward recommendations which would reduce the average radiation exposure.

Patients & Methods: A retrospective review was performed for patients admitted between January 2011 and February 2012 to two acute hospitals on the Hong Kong Island, who had both KUB and non-contrast computed tomography (NCCT) performed for the investigation of loin pain. The accuracy of KUB was determined using NCCT as the gold standard.

Results: Urolithiasis was detected on NCCT in 458 patients out of 891 patients evaluated. The sensitivity, specificity, positive predictive value and negative predictive value of KUB were 46.9%, 95.8%, 92.3% and 63.1% respectively. In in-patient setting, if NCCT was employed as the first-line investigation, omission of KUB in patients with no urolithiasis would result in 4.4% reduction in radiation exposure. In out-patient setting, if KUB was employed as the first-line investigation, the high positive predictive value would justify non-invasive stone management without confirmation by NCCT. The omission of NCCT resulted in 23.8% reduction in radiation exposure.

Conclusion: KUB had low sensitivity, but high positive predictive value for the detection of urolithiasis. Targeted and judicious employment of imaging modality reduced radiation exposure.