Lantz H, Samuelson G, Bratteby L E, Mallmin H, Sjöström L
Department of Medicine, Sahlgrenska University Hospital, Göteborg, Sweden.
Int J Obes Relat Metab Disord. 1999 Jul;23(7):764-70. doi: 10.1038/sj.ijo.0800905.
To compare bone mineral and body composition results of two dual-energy X-ray absorptiometry (DXA) instruments from the same manufacturer.
The Medical departments of Sahlgrenska University Hospital, Göteborg and University Hospital, Uppsala, Sweden.
Unique aluminium spine phantoms (Phant A and B) delivered with each DXA machine (DXA-A and DXA-B) were cross-checked on the other machine by using the 'AP spine mode'. Eight adolescents were examined on both instruments within 5 h to ascertain total body variables by using standard, as well as extended, modes of analysis. All these double-examinations were undertaken on two occasions, before and after exchange of a detector on the DXA-B.
Four males and four females aged 15.4-19.2 y with normal body weights, were examined on both occasions. On each occasion, the first examination was performed in Göteborg on four individuals and in Uppsala on four individuals.
On the first occasion the phantom measurements resulted in much lower bone mineral density (BMD) values on the DXA-B than on the DXA-A. Later it was detected that a so-called R-value and the corresponding '%-fat' value were out of range on the DXA-B. After exchange of detector, the difference in phantom BMD-values between the two machines had diminished. On the first occasion in vivo BMD values were lowest on the DXA-B (P < 0.01), while on the second occasion they were significantly lower on the DXA-A (P < 0.05). Soft tissue differences were greater after detector exchange and as compared to DXA-A, DXA-B underestimated body fat by 3.5 kg (13.2 vs 9.7 kg, P < 0.001) and overestimated lean tissue mass by 3.8 kg (47.1 vs 50.9 kg, P < 0.001) on the second occasion.
The differences in results between two apparently identical Lunar DPX-L machines were not acceptable. In multicenter studies, it may be necessary to standardise results of participating machines into results of one machine by means of regression equations obtained by examining subsamples of individuals on one master machine and other participating instruments.
比较同一制造商生产的两台双能X线吸收仪（DXA）的骨矿物质和身体成分测量结果。
瑞典哥德堡萨尔格伦斯卡大学医院和乌普萨拉大学医院的医学科室。
随每台DXA机器（DXA - A和DXA - B）提供的独特铝制脊柱体模（体模A和体模B），通过使用“前后位脊柱模式”在另一台机器上进行交叉检查。8名青少年在5小时内在两台仪器上接受检查，以使用标准以及扩展分析模式确定全身变量。所有这些双重检查在DXA - B的探测器更换前后分两次进行。
4名男性和4名女性，年龄在15.4 - 19.2岁之间，体重正常，两次检查均参与。每次检查时，在哥德堡对4名个体进行首次检查，在乌普萨拉对4名个体进行首次检查。
第一次检查时，体模测量结果显示DXA - B上的骨矿物质密度（BMD）值远低于DXA - A。后来发现DXA - B上的所谓R值和相应的“脂肪百分比”值超出范围。更换探测器后，两台机器之间体模BMD值的差异减小。第一次检查时，活体BMD值在DXA - B上最低（P < 0.01），而第二次检查时在DXA - A上显著更低（P < 0.05）。探测器更换后软组织差异更大，与DXA - A相比，第二次检查时DXA - B低估体脂3.5千克（13.2对9.7千克，P < 0.001），高估瘦组织质量3.8千克（47.1对50.9千克，P < 0.001）。
两台表面上相同的Lunar DPX - L机器之间的结果差异是不可接受的。在多中心研究中，可能有必要通过在一台主机器和其他参与仪器上检查个体子样本获得的回归方程，将参与机器的结果标准化为一台机器的结果。
