Objective To investigate the proportion , risk factors and tendency of change of stone composition in recurrent urolithiasis .Methods Eighty-five recurrent urolithiasis patients from 2002 to 2014 were enrolled in this retrospective cohort study .There were 61 male and 24 female patients with a median age of 51 (21-89) years at initial events.Among those patients, 70 had two events, 12 had three events, and 3 had more than 3 events.Compositions of initial and recurrent stones were measured by infrared spectrophotometry.Stone type, recurrence interval and recurrence frequency were studied as potential risk factors for composition change . Chi square test and logistic regression analysis were employed in the statistical analysis.Results Stone composition changed during recurrence in 26 patients ( 30.6%) . Univariate analysis showed the risk ratio of composition change in the patients with recurrence interval of 1-5 years was 0.518 (95%CI, 0.277-0.967, P<0.05) when compared with those of less than 1 year or more than 5 years.Logistic regression analysis showed the odds ratio of recurrence interval of 1-5 years was 0.231 (95%CI, 0.075-0.707, P=0.010).The mutual conversion between calcium oxalate and infection stones was mostly observed when stone composition changed during recurrence .Twenty percent of calcium oxalate stones changed to infection stones and 29.2% of infection stones changed to calcium oxalate .
Conclusions Stone composition changes in about one third patients of recurrent urolithiasis .The mutual conversion between calcium oxalate and infection stones is the most common change .Recurrence interval is an independent risk factor to predict composition change .Repeated stone analysis should be suggested to patients with recurrent interval of less than 1 year or more than 5 years.

Objective To investigate if distribution of stone composition and onset age in the upper urinary tract changed during the past 12 years in China.Methods There were 1 878 urolithiasis patients of the upper urinary tract in our hospital from 2003 to 2014 enrolled in present cross-sectional study.There were 1 300 male and 578 female patients with a median onset age of 46 (6-95) years.Stone composition was measured by infrared spectrophotometry.All the patients were divided into 3 groups according to the onset year:Year 2003-2006,Year 2007-2010 and Year 2011-2014.The distributions of stone types were compared among the 3 groups.Age and gender were included as potential confounders.Chi square test,P trend test,Kruskal-Wallis test and logistic regression were employed in the statistical analysis.Results Calcium oxalate was the most common type with a dominant proportion of 78.1％ (1 466/1 878),while uric acid had a small proportion of 4.8％ (91/1 878).The proportions of uric acid in the 3 groups were 2.7％ (12/441),5.1％ (39/758) and 5.9％ (40/679),showing an increasing trend (P ＜0.05).Multivariate analysis showed that year group was independently correlated with the proportion of uric acid,with an OR of 1.385 (95％ CI,1.027-1.867).From 2003 to 2014,the proportion of uric acid calculus increased by 0.42％ (95％ CI,0.25％-0.59％) annually.The median ages of disease onset were 43,46 and 49 years respectively in those three groups,also showing an increasing trend with time (P ＜0.01).Conclusion From 2003 to 2014,the proportion of uric acid and onset age in patients of upper urinary tract calculi were increased in the present cohort.