Lohman T G, Harris M, Teixeira P J, Weiss L
Department of Exercise and Sport Science, University of Arizona, Tucson 85721, USA.
Ann N Y Acad Sci. 2000 May;904:45-54. doi: 10.1111/j.1749-6632.2000.tb06420.x.
Dual-energy X-ray absorptiometry (DXA) is selected with increasing frequency as a method for both assessing body composition and measuring the changes in body composition. Issues have been raised about hydration, software version, hardware (fan beam vs. pencil beam), and the subject population in relation to the validity of DXA-derived estimates of body composition. This paper reviews validation studies of DXA to assess the impact of recent developments in its technology. Studies by Prior et al., Kohrt et al., Salamone et al., Going et al., and Pietrobelli et al. demonstrate the effectiveness of DXA estimates of changes in body composition. By contrast, Clasey et al., Nelson et al., and Friedl et al. found limitations in DXA estimates of body composition and its changes. These contradictory conclusions were explored for threats to internal validity in each research study. From this analysis, two validation guidelines are recommended for use when evaluating estimates of body composition. When multicomponent models are used, it is essential that estimates of body water as a fraction of fat-free mass fall in the expected range (71 to 75%) and have a relatively small standard deviation (2 to 3%). For measuring changes in body composition, DXA estimates of total body mass must accurately reflect both baseline and posttreatment scale body weight estimates. Failure to meet these guidelines threatens the internal validity of the study and raises the likelihood of methodological discrepancies. Applying these criteria to DXA studies of body composition under review accounts for much of the contradictory conclusions among investigations.
双能X线吸收法（DXA）越来越频繁地被选作评估身体成分及测量身体成分变化的方法。关于水合作用、软件版本、硬件（扇形束与笔形束）以及与DXA得出的身体成分估计值有效性相关的研究对象群体等问题已被提出。本文回顾了DXA的验证研究，以评估其技术最新进展的影响。普赖尔等人、科尔特等人、萨拉莫内等人、戈英等人以及彼得罗贝利等人的研究证明了DXA对身体成分变化估计的有效性。相比之下，克拉西等人、纳尔逊等人以及弗里德尔等人发现DXA在身体成分及其变化的估计方面存在局限性。针对每项研究中内部效度的威胁因素，探讨了这些相互矛盾的结论。通过该分析，推荐了两条验证指南用于评估身体成分估计值。当使用多成分模型时，身体水分占去脂体重的比例估计值必须落在预期范围内（71%至75%）且标准差相对较小（2%至3%），这一点至关重要。为测量身体成分的变化，DXA对总体重的估计值必须准确反映基线和治疗后秤量的体重估计值。未能满足这些指南会威胁研究的内部效度，并增加方法学差异的可能性。将这些标准应用于正在审查的身体成分DXA研究，解释了各调查之间许多相互矛盾的结论。
