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.