<p>Population-specific reference data are required to interpret growth measurements in children. Sitting height and leg length (standing height minus sitting height) measurements are indicators of proportionality and can be used to evaluate children with disordered growth. NHANES III recorded sitting height and standing height measurements in a strategic random sample of the United States population from 1988 to 1994, and we have previously published reference charts for sitting height to standing height ratio in this population. In this study, we have developed separate sitting height and leg length reference charts for Non-Hispanic Black, Non-Hispanic White, and Mexican-American children in the United States. In addition, we provide mean (SD) and LMS data to support the use of these reference charts in clinical care.</p>

<p><strong>OBJECTIVE: </strong>To create reference charts for Sitting height to standing height ratio (SitHt/Ht) for children in the United States, and to describe the trajectory of SitHt/Ht during puberty.</p>

<p><strong>STUDY DESIGN: </strong>This was a cross-sectional study using data from the 1988-1994 National Health and Nutrition Examination Survey III, a strategic random sample of the United States population. Comparison between Non-Hispanic White (NHW), Non-Hispanic Black (NHB) and Mexican American groups was performed by analysis of variance (ANOVA) to determine if a single population reference chart could be used. ANOVA was used to compare SitHt/Ht in pre-, early and late puberty.</p>

<p><strong>RESULTS: </strong>NHANES III recorded sitting height and standing height measurements in 9,569 children aged 2 to 18 years of NHW (n=2,715), NHB (n=3,336), and Mexican American (n=3,518) ancestry. NHB children had lower SitHt/Ht than NHW and Mexican American children throughout childhood (p &lt; 0.001). In both sexes, SitHt/Ht decreased from prepuberty to early puberty and increased in late puberty. Sex-specific percentile charts of SitHt/Ht vs age were generated for NHB and for NHW and Mexican American youth combined.</p>

<p><strong>CONCLUSIONS: </strong>SitHt/Ht assessment can detect disproportionate short stature in children with skeletal dysplasia, but age-, sex- and population-specific reference charts are required to interpret this measurement. NHB children in the United States have significantly lower SitHt/Ht than other children, which adds complexity to interpretation. We recommend the use of standardized ancestry-specific reference charts in screening for skeletal dysplasias and have developed such charts in this study.</p>

<p>Annual gains in BMC and areal bone mineral density (aBMD) in children vary with age, pubertal status, height-velocity, and lean body mass accrual (LBM velocity). Evaluating bone accrual in children with bone health-threatening conditions requires consideration of these determinants. The objective of this study was to develop prediction equations for calculating BMC/aBMD velocity SD scores (velocity-Z) and to evaluate bone accrual in youth with health conditions. Bone and body compositions via DXA were obtained for up to six annual intervals in healthy youth (n = 2014) enrolled in the Bone Mineral Density in Childhood Study (BMDCS) . Longitudinal statistical methods were used to develop sex- and pubertal-status-specific reference equations for calculating velocity-Z for total body less head-BMC and lumbar spine (LS), total hip (TotHip), femoral neck, and 1/3-radius aBMD. Equations accounted for (1) height velocity, (2) height velocity and weight velocity, or (3) height velocity and LBM velocity. These equations were then applied to observational, single-center, 12-month longitudinal data from youth with cystic fibrosis (CF; n = 65), acute lymphoblastic leukemia (ALL) survivors (n = 45), or Crohn disease (CD) initiating infliximab (n = 72). Associations between BMC/aBMD-Z change (conventional pediatric bone health monitoring method) and BMC/aBMD velocity-Z were assessed. The BMC/aBMD velocity-Z for CF, ALL, and CD was compared with BMDCS. Annual changes in the BMC/aBMD-Z and the BMC/aBMD velocity-Z were strongly correlated, but not equivalent; LS aBMD-Z = 1 equated with LS aBMD velocity-Z = -3. In CF, BMC/aBMD velocity-Z was normal. In posttherapy ALL, BMC/aBMD velocity-Z was increased, particularly at TotHip (1.01 [-.047; 1.7], p &lt; 0.0001). In CD, BMC/aBMD velocity-Z was increased at all skeletal sites. LBM-velocity adjustment attenuated these increases (eg, TotHip aBMD velocity-Z: 1.13 [0.004; 2.34] versus 1.52 [0.3; 2.85], p &lt; 0.0001). Methods for quantifying the BMC/aBMD velocity that account for maturation and body composition changes provide a framework for evaluating childhood bone accretion and may provide insight into mechanisms contributing to altered accrual in chronic childhood conditions. © 2018 American Society for Bone and Mineral Research.</p>