Albertine Donker

TSAT/Hepcidin Ratio discriminates TMPRSS6 -related Anemia from IDA 281 8 Statistical analysis Descriptive statistics were reported as medians, 25th to 75th percentiles (Interquartile Range, IQR), and/or ranges for continuous variables and as absolute frequencies and percentages for categorical variables, using original untransformed values. Normality of distributions of the continuous variables was visually checked using histograms. Baseline characteristics between the IRIDA group and the non-IRIDA group were compared and tested by using the Chi-squared test for categorical variables and the Mann-Whitney U test for continuous variables to determine whether there were significant differences between the groups. Measurements of hepcidin levels and the TSAT/hepcidin ratio were stratified by sex with for female subjects a distinction between premenopausal and postmenopausal age for female subjects. In addition, in the IRIDA group a distinction was made between children and adults, since sex- and age-specific differences in hepcidin levels have been previously described between children and adults. 34 33 Hepcidin values below the lower limit of detection (<0.5 nM) were imputated with the average value of 0.25 nM. We assessed the performance of the TSAT/hepcidin ratio in distinguishing TMPRSS6- related IRIDA from TMPRSS6 -unrelated IDA by Receiver Operating Characteristic (ROC) analysis. In order to avoid negative values, we used the TSAT/hepcidin ratio, instead of the TSAT/loghepcidin ratio as others did. 14 The area under the curve (AUC) was calculated, including the sensitivity and specificity for each possible cut-off point of the TSAT/hepcidin ratio. An AUC value of 1 represents the perfect discriminating test. The Youden index ([sensitivity + specificity -1]) was used to select the optimal cut-off value. 35 P values less than 0.05 were considered statistically significant. SPSS version 22 was used for data analysis.