Statistical Analyses
Statistical analyses were performed using SPSS 13.0 software (SPSS Inc., Chicago, Illinois, USA). The Kolmogorov-Smirnov test was used to analyze the normality of the distribution of parameters. Continuous variables are expressed mean±SD, while categorical variables are expressed as a number (percentage). Comparison between 2 groups using the t test or chi-squared test. Nonparametric variables are described as medians and quartile ranges, and the comparisons between groups were made using
the Mann-Whitney test or the Kruskal-Wallis test. Patients were classified into C3low and C3high groups by grading the density of glomerular C3 deposition. The descriptive analysis of the time reaching the primary and secondary endpoint was performed by computing survival curves according to the Kaplan-Meier method, and between-group survival was compared by the log-rank test. Univariate and multivariate Cox proportional hazards models were used to determine the factors associated with the risk of reaching the creatinine doubling from baseline (multifailure model) or ESRD. Results were expressed as hazard-rate (HRs) with CI. Univariate and multivariate linear regression analyses were used to determine the associations between the density of glomerular C3 deposition and other variables that correlate with renal outcome. The multivariate models were built considering that the main interest was the identification of prognostic factors, present at the enrollment and statistically significant at univariate analysis. Two-sided P values <0.05 were considered statistically significant.