The Relationship of Obesity and Gender Prevalence Changes in United States Inpatient Nephrolithiasis

ObjectiveTo review the Nationwide Inpatient Sample database to examine the relationships between obesity, gender, and nephrolithiasis. Recent reports indicate that the prevalence of nephrolithiasis has been increasing, especially among women.MethodsThe Nationwide Inpatient Sample contains data on approximately 20% of hospital stays in the United States. Included in this analysis were discharges with primary diagnosis ICD-9 codes 592.0 (renal calculus) or 592.1 (ureteral calculus), from 1998 through 2003. All raw data were weighted to produce national estimates. Descriptive and inferential statistics were performed to determine changes in nephrolithiasis prevalence and associations of obesity and other comorbidities with nephrolithiasis.ResultsWe reviewed 181,092,957 hospital stays (weighted data). The prevalence of nephrolithiasis was relatively stable: 0.52% (149,302) in 1998 and 0.47% (147,541) in 2003. The prevalence of obesity increased from 3.06% (878,155) to 4.99% (1,575,247). The male:female ratio of patients with stones decreased from 1.6:1 to 1.2:1. Multivariate analysis revealed a statistically significant relationship (OR = 1.22, 95% CI 1.20–1.23, P <.001) between obesity and urinary stones. Obese females were more likely to develop stones than nonobese females (OR = 1.35, 95% CI 1.33–1.37, P <.001). The association between obesity and stones was weaker in males (OR = 1.04, 95% CI 1.02–1.06, P <.001).ConclusionIn this sample of inpatients, obesity was associated with a significantly increased prevalence of urinary stones. This relationship was stronger in females than in males. Further studies are needed to determine whether weight reduction in obese patients affects urinary stone disease.