To investigate the prevalence of nephrolithiasis in gouty patients by computed tomography (CT) imaging and to compare it with the "prevalence" of urolithiasis calculated from histories of urinary tract calculus.
The kidneys of 383 male patients with primary gout were examined using an unenhanced 2-row helical CT detector, imaging at 2 mm collimation and a helical pitch of 3. The urolithiasis history of the 383 patients was investigated by inquiry. Patients' ages, body mass index, and laboratory data from a 1-hour clearance test were determined.
CT scans confirmed nephrolithiasis in 103 (26.9%, 95% confidence interval 22.5%-31.6%) of the 383 gouty patients, and history of urinary calculus was positive in 65 (17.0%, 95% confidence interval 13.4%-21.1%) of the 383. However, 64 (62%) of the 103 stone-formers identified by CT had no history of urolithiasis. There was a significant difference between the ages of the 103 stone-formers identified by CT and the 65 stone-formers identified from the history.
The prevalence of nephrolithiasis obtained using CT was 26.9% in the 383 patients with primary gout. Our results imply that we cannot determine an accurate prevalence of urolithiasis from a patient's history. Most of the "prevalence" reported in the past may not correspond to a statistically justifiable one, but instead to the "cumulative incidence" during the contraction period of gout. Thus, the prevalence of nephrolithiasis confirmed by a cross-sectional method and the "prevalence" of urolithiasis calculated from patients' calculus histories should be clearly distinguished.