Statistical analysis
Categorical variables were expressed as numerals and percentages and were compared with χ2 tests. Continuous variables were expressed as mean ± SD and were compared using the unpaired Student’st test or the Mann-Whitney U test based on distribution.
Unadjusted overall time to initiation of dialysis was indicated by Kaplan-Meier analysis with log-rank testing. Cox proportional hazards regression model identified variables related to the initiation of dialysis. Covariates included traditional risk factors for dialysis in each model. Hypertension as a covariate was determined according to SBP diagnosed by seven different cut-offs (i.e., ≥110 mmHg, ≥115 mmHg, ≥120 mmHg, ≥125 mmHg, ≥130 mmHg, ≥140 mmHg, and ≥150 mmHg). Data were compared among 10 groups of participants divided according to combinations of the presence or absence of DM and five stratified levels of SBP (i.e., ≤119 mmHg, 120-129 mmHg, 130-139 mmHg, 140-149 mmHg, and ≥150 mmHg).
Analyses were performed using SPSS (version 19.0, IBM, Chicago, IL, USA). Statistical significance was considered for P <0.05. The Ethics Committee of the Niigata University approved this study.