The Prevalence of Nephrolithiasis in Patients with Primary Gout: a Cross-sectional Study Using Helical Computed Tomography

Objective: 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.

Methods: 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.

Results: 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.

Conclusion: 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.