Statistical analyses
Statistical analysis was performed by SPSS V22.0 (IBM Software, Armonk, NY, USA). Measurements and indexes are expressed as mean ± SD. Continuous variables are described as mean ± standard deviation and were compared using Student’s t-test. Categorical variables are presented as percentages and were analyzed using Fisher’s exact test. A receiver operating characteristic (ROC) curve was plotted to evaluate the validity and the boundary value was calculated. A P < 0.05 was considered statistically significant.