Sitting Height to Standing Height Ratio Reference Charts for Children in the United States.

OBJECTIVE: 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.

STUDY DESIGN: 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.

RESULTS: 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 < 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.

CONCLUSIONS: 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.