Statistical analysis
The analyses were performed in SPSS Statistics for Windows version 23
(IBM Corp., Armonk, NY, USA). The average concentrations of Hb, ferritin
and 25OHD over one year period prior to the study were used for the
analysis. Data distribution was assessed before performing the analyses.
Descriptive statistics are presented as number (percentage), mean ± SD
or median (Q1-Q3), as appropriate. The χ2 or Fisher’s exact test was
used for the comparison of proportions. Participants were stratified
according to tertiles of Dkk-1 concentration [low: range
<197 pg/mL, mid: 197-523 pg/mL, high: >523
pg/mL]. For the group comparison, a t-test, one-way ANOVA or one-way
analysis of covariate (ANCOVA) was used for normally distributed data,
and a Mann-Whitney U test or Kruskal-Wallis test was used for skewed
data.
Spearman’s method was used for the correlation analysis. Multivariable
regression models were fit to evaluate the associations between Dkk-1
and BMD z-scores. Participant BA, sex, body mass index (BMI) z-score,
average pre-transfusion Hb and 25OHD concentrations, the history of
delayed puberty, subtype of non-deletional Hb H disease, type of iron
chelator, and prednisolone use were considered as covariates based on
previous data supporting their influences on BMD in
thalassemia.10,25,26 Our analysis was considered
exploratory and hypothesis-generating, therefore, we did not perform
multiple comparisons adjustment. P-value <0.05 was considered
statistically significant.