Height adjustment in assessing dual energy x-ray absorptiometry measurements of bone mass and density in children.

CONTEXT: In children, bone mineral content (BMC) and bone mineral density (BMD) measurements by dual-energy x-ray absorptiometry (DXA) are affected by height status. No consensus exists on how to adjust BMC or BMD (BMC/BMD) measurements for short or tall stature. OBJECTIVE: The aim of this study was to compare various methods to adjust BMC/BMD for height in healthy children. DESIGN: Data from the Bone Mineral Density in Childhood Study (BMDCS) were used to develop adjustment methods that were validated using an independent cross-sectional sample of healthy children from the Reference Data Project (RDP). SETTING: We conducted the study in five clinical centers in the United States. PARTICIPANTS: We included 1546 BMDCS and 650 RDP participants (7 to 17 yr of age, 50% female). INTERVENTION: No interventions were used. MAIN OUTCOME MEASURES: We measured spine and whole body (WB) BMC and BMD Z-scores for age (BMC/BMD(age)), height age (BMC/BMD(height age)), height (BMC(height)), bone mineral apparent density (BMAD(age)), and height-for-age Z-score (HAZ) (BMC/BMD(haz)). RESULTS: Spine and WB BMC/BMD(age)Z and BMAD(age)Z were positively (P < 0.005; r = 0.11 to 0.64) associated with HAZ. Spine BMD(haz) and BMC(haz)Z were not associated with HAZ; WB BMC(haz)Z was modestly associated with HAZ (r = 0.14; P = 0.0003). All other adjustment methods were negatively associated with HAZ (P < 0.005; r = -0.20 to -0.34). The deviation between adjusted and BMC/BMD(age) Z-scores was associated with age for most measures (P < 0.005) except for BMC/BMD(haz). CONCLUSIONS: Most methods to adjust BMC/BMD Z-scores for height were biased by age and/or HAZ. Adjustments using HAZ were least biased relative to HAZ and age and can be used to evaluate the effect of short or tall stature on BMC/BMD Z-scores.