BMD measurement
The total body (TB) and lumbar spine (LS) BMD were measured using GE Lunar Prodigy Advance (GE Healthcare, Madison, WI, USA) densitometer. The areal LSBMD was evaluated on lumbar spine 2-4. Data acquisition and analyses were performed using enCORE software version 18 (SP1). The precision for TBBMD measurement was 0.028 g/cm2 and for LSBMD was 0.028 g/cm2. The z-scores for TBBMD and LSBMD were generated using the normative data for Thai children and adolescents.22 As short stature was prevalent in our study and can produce falsely low BMD, the BMD z-score was expressed as height-for-age adjusted values as previously described.23 The BMD z-score of < -2 was defined as low BMD per the International Society of Clinical Densitometry (ISCD) pediatric position statement.24