Reference Ranges for Body Composition Indices by Dual Energy X-ray Absorptiometry from the Bone Mineral Density in Childhood Study Cohort.

BACKGROUND: Body composition assessment aids evaluation of energy stores and the impact of diseases and interventions on child growth. Current U.S. pediatric reference ranges from the National Health and Nutrition Examination Survey (NHANES) include 20% of children with obesity, BMI ≥95th percentile.

OBJECTIVE: To develop dual energy x-ray absorptiometry (DXA) based reference ranges in a diverse cohort with low obesity prevalence from the Bone Mineral Density in Childhood Study (BMDCS).

DESIGN: This is a secondary analysis of a longitudinal, prospective, observational cohort. Healthy children (height and BMI within 3rd to 97th percentiles, ages 5-19y at enrollment), from 5 U.S. centers were measured annually for up to 7 visits. Whole body scans were acquired using Hologic scanners. A subsample underwent repeat measurements to determine precision. We generated reference ranges for appendicular and total lean soft-tissue mass index (LSTM Index), fat mass index (FMI), and other body composition measures. Resulting curves were compared to NHANES and across subgroups. Sex and age-specific equations were developed to adjust body composition Z-scores for height Z-score.

RESULTS: We obtained 9,846 scans on 2011 participants (51% female, 22% Black, 17% Hispanic, 48% White, 7% Asian/Pacific Islander, 6% with obesity). Precision (percent coefficient of variation) ranged from 0.7 to 1.96%. Median and -2SD curves for BMDCS and NHANES were similar, but NHANES +2SD LSTM Index and FMI curves were distinctly greater than the respective BMDCS curves. Subgroup differences were more extreme for appendicular LSTM Index-Z (mean±sd: Asian -0.52±0.93 vs Black 0.77±0.87) than for FMI-Z (Hispanic 0.29±0.98 vs Black -0.14±1.1) and were smaller for Z-scores adjusted for height Z-score.

CONCLUSIONS: These reference ranges add to sparse normative data regarding body composition in children and adolescents, and are based on a cohort with an obesity prevalence similar to current BMI charts. Awareness of subgroup differences aid in interpreting results.