[Obesity as risk factor for lithiasic recurrence]

Obese patients may have special characteristics in the urinary stones formed, as the body mass index (BMI) may also be a predictive factor in lithiasic recurrence. We aim to evaluate and compare the lithiasic characteristics according to the different BMI categories, also considering the likelihood of lithiasic recurrence in presence of age and gender covariables.

Retrospective, cross-sectional analysis on 346 lithiasic patients, 96 (27.7%) had low-normal weight, 151 (43.6%) overweight, and 99 (28.6%) obesity. The Chi-square and ANOVA tests were used. Survival analysis for the calculation of likelihood of lithiasic recurrence (yes/no) was made based on time on 158 patients in whom complete resolution of the initial stone was achieved by the Kaplan Meier method. Comparisons between the different categories of BMI were made using the log-Rank, Breslow and Tarone-Ware tests. Multivariate analysis was also made with the Cox regression model, introducing the covariables of age and gender.

A significant growing linear tendency has been demonstrated between multiplicity and BMI (p=0.03). The variables size and composition did not show significant differences between the groups. Median follow-up of 158 patients included in the survival analysis was 1866 days (95% CI 1602.5-2129.5). Eighteen (11.4%) of them recurred, without finding significant differences between groups: 4 low-normal weight (9.8%), 10 overweight (14.1%) and 4 obese (8.7%). The multivariate analysis also did not show a significant influence of the BMI on lithiasic recurrence (p=0.86; HR =1.06; 95% CI: 0.56-2.03).

A significant influence of BMI was shown on lithiasic multiplicity on diagnosis, although not on lithiasic recurrence based on time. It seems to be necessary to carry out studies in larger samples to calculate the true influence of BMI on lithiasic recurrence.