A proposal for the adjustment of bone mineral density for body dimensions in children.

Objectives: The precise age estimation is of high importance in bone mineral density (BMD) assessment in children, since the bone structure of a studied child is evaluated by using the age and gender dependent references. In addition, the biological age - the bone age in this case - estimation could help this bone structural evaluation process, since the developmental status of the skeletal system can significantly alter from the theoretical developmental status determined by chronological age in healthy, but early or late maturing children. The aims of the study were (1) to check whether volumetric BMD (vBMD) Z-scores estimated by considering chronological age and biological age differ significantly in children aged between 7-18 years, and (2) in the case of significant inaccuracy of Z-score estimation based on chronological age to construct new vBMD standards adjusted for body developmental status. Subjects and methods: Body structural and densitometry data of 476 healthy children aged between 7 and 18 years were used in the analysis. pQCT measurements were performed at the distal radius using Stratec XCT-2000 equipment (Stratec Inc, Germany). The centile curves of vBMD parameters were estimated by using lmsChartMaker Pro 2.3 software. Ulnar length age was used as biological age in the analysis. Results: The total and 'cortical + subcortical' vBMD changed by age in the studied age interval in both genders, while the trabecular vBMD showed significant change by age only in females. Our results confirmed that when the biological age of a child significantly differs from her/his chronological age, vBMD evaluation should be done by considering her/his biological age. Due to the increase in individual variability of rate and timing of pubertal developmental processes, the sensitivity of vBMD evaluation by considering body developmental status was the lowest in the age between 12 and 16 years in the boys and between 10 and 12 years in the girls. Therefore the suggested vBMD adjustments for biological ages are highly recommended to use at least in children with ages outside these age intervals. Conclusion: If the estimation of any biological age cannot be carried out, vBMD references adjusted for height or other body dimensions should be used in the bone health status estimation in children.