Speakman J R, Booles D, Butterwick R
Aberdeen Centre for Energy Regulation and Obesity, Department of Zoology, University of Aberdeen, Aberdeen, Scotland, UK.
Int J Obes Relat Metab Disord. 2001 Mar;25(3):439-47. doi: 10.1038/sj.ijo.0801544.
Dual-energy X-ray absorptiometry (DXA) has been used extensively to measure body composition, but has been validated by comparison to chemical analysis on relatively few occasions. Moreover, these previous validation studies have ground up entire carcasses prior to chemical analysis, thus potentially obscuring sources of error in the DXA analysis.
The purpose of this study was to validate DXA by comparison to chemical analysis in dogs and cats, performing chemical analysis on dissected rather than ground carcasses to reveal sources of discrepancy between the two methods.
Sixteen animals (10 cats and 6 dogs weighing between 1.8 and 22.1 kg) were scanned by DXA post-mortem using a Hologic QDR-1000 W pencil beam machine and then dissected into 22 separate components. Individual tissues were dried and then sub-sampled for analysis of fat content by Soxholet extraction, or ashing in a muffle furnace. Body composition by DXA was compared to body composition by chemical analysis and discrepancies between the two correlated with chemical composition of individual tissues. We also explored the capability of the machine to establish the fat contents of mixtures of ground beef, lard and water.
DXA estimates were strongly correlated with estimates derived from chemical analysis: total body mass (r=1.00), lean tissue mass (r=0.999), body water content (r=0.992) and fat mass (r=0.982). Across individuals the absolute and percentage discrepancies were also small: total body mass (13.2 g, 1.02%), lean tissue mass (119.4 g, 2.64%), water content (101 g, 1.57%) and fat content (28.5 g, 2.04%), where the percentage error is expressed relative to the average mass of that component across all individuals. Although on average DXA compared very well to chemical analysis, individual errors were much greater. Individual errors in the lean tissue and fat tissue components were strongly correlated with the fat content of skeletal muscle and the lean content of mesenteric fat. The error in the DXA estimate of total fat content was related to skeletal muscle hydration. Experimental studies using mixtures of lean ground beef, water and lard indicated that tissue hydration may have important effects on the perception of tissue fat content by DXA. Bone mineral content by DXA was approximately 30% lower than whole body ash content but only 7.7% lower than ash content of the bones.
On average pencil beam DXA analysis using the Hologic QDR-1000 W machine provides an accurate estimate of body composition in subjects weighing between 1.8 and 22.1 kg. Individual discrepancies, however, can be large and appear to be related to lean tissue hydration.
双能X线吸收法（DXA）已被广泛用于测量身体成分，但与化学分析相比，其仅在相对较少的情况下得到验证。此外，这些先前的验证研究在化学分析之前将整个尸体磨碎，从而可能掩盖了DXA分析中的误差来源。
本研究的目的是通过与犬猫的化学分析相比较来验证DXA，对解剖后的而非磨碎的尸体进行化学分析，以揭示两种方法之间的差异来源。
对16只动物（10只猫和6只狗，体重在1.8至22.1千克之间）进行死后DXA扫描，使用Hologic QDR - 1000 W笔形束机器，然后将其解剖为22个单独的部分。将各个组织干燥，然后进行子采样，通过索氏提取法分析脂肪含量，或在马弗炉中灰化。将DXA得出的身体成分与化学分析得出的身体成分进行比较，并将两者之间的差异与各个组织的化学成分相关联。我们还探索了该机器测定碎牛肉、猪油和水混合物脂肪含量的能力。
DXA估计值与化学分析得出的估计值高度相关：总体重（r = 1.00）、瘦组织质量（r = 0.999）、身体水分含量（r = 0.992）和脂肪质量（r = 0.982）。在个体中，绝对差异和百分比差异也很小：总体重（13.2克，1.02%）、瘦组织质量（119.4克，2.64%）、水分含量（101克，1.57%）和脂肪含量（28.5克，2.04%），其中百分比误差是相对于所有个体中该成分的平均质量而言的。尽管平均而言DXA与化学分析的比较效果很好，但个体误差要大得多。瘦组织和脂肪组织成分中的个体误差与骨骼肌的脂肪含量和肠系膜脂肪的瘦组织含量密切相关。DXA对总脂肪含量估计的误差与骨骼肌水合作用有关。使用瘦碎牛肉、水和猪油混合物的实验研究表明，组织水合作用可能对DXA对组织脂肪含量的感知有重要影响。DXA测得的骨矿物质含量比全身灰分含量低约30%，但仅比骨骼灰分含量低7.7%。
平均而言，使用Hologic QDR - 1000 W机器进行笔形束DXA分析能够准确估计体重在1.8至22.1千克之间的受试者的身体成分。然而，个体差异可能很大，并且似乎与瘦组织水合作用有关。
