Statistical analysis
The continuous variables are summarized as the means±SD, and categorical variables as proportions. The differences between the patients with and without preexisting anemia were examined with the use of Pearson Chi-Square test or Fisher’s exact test for categorical variables, or Student t-test or Mann-Whitney U test for continuous variables. Univariate and multivariate logistic regression models were used to determine the factors independently associated with the primary endpoint. Likely parameters were included as explanatory variables in the univariate models. For some continuous variables included in the models, the cut-off points were determined according to their upper or lower normal limits, otherwise, the medians. Variables with a P value of <0.1 in the univariate analyses were further included in the multivariate models. All statistical analyses were performed with the use of JMP software version 13.0 (SAS Institute, Cary, NC, USA). A P value of <0.05 was considered significant.