Reference ranges for body composition indices by dual energy X-ray absorptiometry from the Bone Mineral Density in Childhood Study Cohort

Abstract

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

Objectives: This study aimed 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).

Methods: This is a secondary analysis of a longitudinal, prospective, observational cohort. Healthy children (height and BMI within 3rd to 97th percentiles, ages 5-19 y at enrollment), from 5 United States centers were measured annually for ≤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 9846 scans of 2011 participants (51% female, 22% Black, 17% Hispanic, 48% White, 7% Asian/Pacific Islander, and 6% with obesity). Precision (percent coefficient of variation) ranged from 0.7% to 1.96%. Median and-2 standard deviation curves for BMDCS and NHANES were similar, but NHANES +2 standard deviation 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 compared with Black 0.77 ± 0.87) than for FMI-Z (Hispanic 0.29 ± 0.98 compared with 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 aids in interpreting results.

Keywords: DXA; fat mass index; lean soft tissue mass index; pediatric; reference.

FIGURE 1

Consort diagram showing enrollment of study participants and exclusions that resulted in the final data set used to create body composition reference ranges. IBD, inflammatory bowel disease.

FIGURE 2

Comparison of (A) lean soft tissue mass index and (B) fat mass index distributions for the Bone Mineral Density in Childhood Study (black lines) and the NHANES (1999–2004) published by Weber et al. [11]. Shown are the reference curves for −2 SD, 0 SD, and +2 SD for each source. Reference ranges are not based on the NHANES body composition adjustment.

FIGURE 3

Scatterplots and regression lines illustrating the relationships of height-for-age Z-score (HAZ) with appendicular lean soft tissue mass (LSTM) index-Z score (A), appendicular LSTM-Z score (B), HAZ-adjusted appendicular LSTM (C), and fat mass index-Z score (FMI-Z) (D) by age group. R-square values were determined by mixed effects regression for each age group (Ages 5 to 9.9 y, n = 2130 observations; Ages 10–14.9 y, n = 3920 observations; Ages 15–19.9 y, n = 3069 observations). Appendicular LSTM index-Z score had a modest association with height-for-age Z-score at younger ages but not for 15- to 20-y-olds. Appendicular LSTM-Z score had a very strong association with HAZ at all ages, providing the rationale for the HAZ adjustment equations. FMI-Z score was positively associated with HAZ in younger children and negatively associated with HAZ in older children, but the associations were modest.

FIGURE 4

Mean Z-scores by self-identified race and ethnicity groups for height-for-age, BMI, appendicular lean soft tissue mass index and HAZ-adjusted appendicular lean soft tissue mass. Note that height and BMI Z-scores were calculated using the CDC 2000 reference [4]. CDC, Centers for Disease Control and Prevention; HAZ, height-for-age Z-score.