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.