Characteristics of gout patients according to the laterality of nephrolithiasis: A cross‐sectional study using helical computed tomography

OBJECTIVE: To clarify the clinical and laboratory characteristics of nephrolithiasis in gout by computed tomography (CT). METHODS: In 350 gout patients, unenhanced CT was performed at the 1st visit to hospital. Calculus density spots exceeding 1 mm in diameter with a CT value >120 Hounsfield units in the kidneys were defined as kidney stones. The association between laterality and the number of stones was investigated in each stone carrier. The 350 patients were classified into three groups (bilateral, unilateral and non-stone carriers). Then serum urate (Sua), renal function, uric acid metabolism, and the prevalence of metabolic syndrome (Mets) were compared among these groups by the Tukey-Kramer test or Fisher's exact test. RESULTS: Kidney stone(s) were detected in 108 (31%) of the 350 patients (bilateral in 58 and unilateral in 50). In 64 of the 108 patients (59%), there was no history of urolithiasis. Sua, serum creatinine and uric acid clearance were significantly higher (P = 0.001, P < 0.001, P = 0.043, respectively), while the estimated glomerular filtration rate was significantly lower (P = 0.039) in bilateral stone carriers than in non-stone carriers. No significant differences of uric acid metabolism or the prevalence of Mets were noted among the three groups. CONCLUSIONS: Approximately one-third of gout patients had kidney stones and more than half of the patients with stones were bilateral and multiple stone carriers. Elevation of Sua might increase the stone burden in gout, leading to more severe renal dysfunction. An association between nephrolithiasis and Mets was not demonstrated in gout patients.