Testolin C G, Gore R, Rivkin T, Horlick M, Arbo J, Wang Z, Chiumello G, Heymsfield S B
Department of Pediatrics, San Raffaele Hospital, 20132 Milano, Italy.
J Appl Physiol (1985). 2000 Dec;89(6):2365-72. doi: 10.1152/jappl.2000.89.6.2365.
Dual-energy X-ray absorptiometry (DXA) percent (%) fat estimates may be inaccurate in young children, who typically have high tissue hydration levels. This study was designed to provide a comprehensive analysis of pediatric tissue hydration effects on DXA %fat estimates. Phase 1 was experimental and included three in vitro studies to establish the physical basis of DXA %fat-estimation models. Phase 2 extended phase 1 models and consisted of theoretical calculations to estimate the %fat errors emanating from previously reported pediatric hydration effects. Phase 1 experiments supported the two-compartment DXA soft tissue model and established that pixel ratio of low to high energy (R values) are a predictable function of tissue elemental content. In phase 2, modeling of reference body composition values from birth to age 120 mo revealed that %fat errors will arise if a "constant" adult lean soft tissue R value is applied to the pediatric population; the maximum %fat error, approximately 0.8%, would be present at birth. High tissue hydration, as observed in infants and young children, leads to errors in DXA %fat estimates. The magnitude of these errors based on theoretical calculations is small and may not be of clinical or research significance.
双能X线吸收法（DXA）对脂肪百分比（%）的估计在幼儿中可能不准确，因为幼儿通常具有较高的组织水合水平。本研究旨在全面分析儿科组织水合作用对DXA脂肪百分比估计值的影响。第一阶段为实验阶段，包括三项体外研究，以建立DXA脂肪百分比估计模型的物理基础。第二阶段扩展了第一阶段的模型，由理论计算组成，以估计先前报道的儿科水合作用产生的脂肪百分比误差。第一阶段的实验支持了双室DXA软组织模型，并确定了低能量与高能量的像素比（R值）是组织元素含量的可预测函数。在第二阶段，对出生至120个月龄的参考身体成分值进行建模，结果显示，如果将“恒定”的成人瘦软组织R值应用于儿科人群，将会出现脂肪百分比误差；最大脂肪百分比误差约为0.8%，出现在出生时。在婴儿和幼儿中观察到的高组织水合作用会导致DXA脂肪百分比估计值出现误差。基于理论计算的这些误差幅度较小，可能不具有临床或研究意义。
