Comparison of patient DXA studies to reference sets is a critical process in the application of DXA studies to a clinical practice. Two areas in which DXA is being extensively applied in clinical practice today are the assessment of bone disease (especially including osteoporosis and osteopenia) and the assessment of body composition disorders (especially fat and lean disorders). Relevant reference population development in DXA studies has typically taken the form of gathering a large enough dataset of relevant studies in the target population to statistically establish an age and sex description of expected distribution. Once a statistically valid description of a population is defined those studies are then applied to assessing the bone or soft tissue condition presented by the subject that is being evaluated.

在将双能量X射线骨密度仪(DXA)应用到临床实践的过程中，将受试者DXA的分析结果与标准的骨密度参考值进行比较是一个关键性的步骤。在今天的临床实践中，DXA被广泛应用于两个领域：一是用于骨病（尤其是骨质疏松症和骨质减少症）的评估，另一个是用于身体成分紊乱（尤其是脂肪和瘦肉含量的紊乱）的评价。在DXA分析研究中，相关的参考群体的发展典型地采用了下面这种形式：通过在目标人群中收集足够多的相关研究资料，在统计学上建立不同年龄和性别的参考人群的预期骨密度分布。一旦在统计学上定义了参考人群骨密度的有效描述，DXA分析方法就可以被用于评价待评估的受试者呈现出的骨状态或软组织状态。

When evaluating the condition presented by the subject undergoing a bone density assessment, subjects undergo assessment of a T-score or Z-score values to grade an individual’s distribution against the “sex matched young adult reference value” or against the “age and sex matched reference value”, respectively. The application of the T-score is then tied to a relative risk of fracture documented by prospective fracture risk studies to determine how subjects might be clinically addressed. Typically the T-score is evaluated as Normal if the T-score value is higher than -1.0 SD, is Osteopenic if the T-score value is between -1.0 SD and -2.5 SD or is Osteoporotic if the T-score is below -2.5 SD (El Maghraoui, A and Roux, C (20108)). The Z-score, alternatively, is evaluated as Normal if the value is within士2.0 SD of the age-matched reference value or as Abnormal if the value is outside the士2.0 SD range when compared to the age-match reference value (Gruber, HE and Baylink, DJ (1981)). Because the reference value comparison is critical to reaching this clinical assessment–to the extent that it is possible一elements that directly impact the clinical concern of fracture risk need to be accommodated for in the reference population. These reference set derive their acceptance from recognition that the relationship exists between bone density and fracture risk and from the use of appropriate population statistics.

当对一个正在接受骨密度评估的受试者呈现出的状态进行评价时，受试者要接受T值评分和Z值评分，继而将评分结果分别与“相应性别青年人的骨密度参考值”和“相应年龄和性别的骨密度参考值”进行对比，从而得出个体的骨密度分布等级。T值的应用之后将会与通过预期骨折风险研究得出的相对骨折风险相联系，进而确定受试者可能要接受的临床治疗方案。通常，当个体骨密度值T值大于-1.0 SD时，则认为个体骨密度正常；当个体骨密度值在-1.0 SD与-2.5 SD之间时，则认为个体骨质减少；当个体骨密度值低于-2.5 SD时，则认为个体骨质疏松(El Maghraoui, A and Roux, C (20108))。同时，如果Z值在同年龄人群参考值的士2.0 SD范围内，则认为正常；如果Z值超出同年龄人群参考值的士2.0 SD范围，则认为不正常(Gruber, HE and Baylink, DJ (1981))。由于将受试者的骨密度值与参考值进行比较是做出临床评价的关键，从这个意义上说，与参考值进行比较的结果可能会直接影响需要提供给参考人群的骨折风险关注度。由于这些参考值承认骨密度和骨折风险之间存在联系，且它们是通过使用合适的人口统计学方法得到的，因此这些参考值具有公认意义。

With regards to assessing fracture risk the gender, age, genetics and health makeup of the reference population dataset have been deemed critical to building a relevant reference set. Obviously gender and age very directly impact the prospect of fracture risk and need to be addressed in the makeup of a relevant reference set. In the same way, the health of your reference population is critical because factors of health will directly impact bone remodeling and cause a decrease in bone density and directly increase relative risk of fracture. In a more subtle way, genetic makeup of the reference population is critical because there is a highly significant link (reflected in a heritability index of 0.69) between genetics and individual bone density (Christian, JC, et al (1989)). This relatively high association with genetics is reported一in large part–to explain the ten percent greater bone density seen in the Black populations than seen in the White populations which seem to have an approximately four percent greater bone density than seen in Asian populations. It is this relatively strong link to genetics that justifies comparing a particular patient to a similar reference population. Ultimately it is a large body of literature that justifies the establishment of reference populations with the best possible similarity to a healthy cohort for the patient being evaluated and that is why manufacturers routinely provide documented and validated reference sets that will match for gender, age and ethnic background with the patient to calculate the relevant T-score and Z-score values.

关于骨折风险的评估，参考人群的性别、年龄、基因遗传学和健康组成被认为是建立一个恰当的参考集合的关键。很明显，性别和年龄会很直接地影响骨折风险的预期，因此需要在相关参考集合的组成中专门提出来。同样，参考人群的健康状况也是至关重要的，因为健康因素会直接影响骨的重建，引起骨密度的降低，从而直接提高骨折的相对风险。更微妙的是，参考人群的基因组成也很关键，因为遗传学和个体的骨密度之间存在重大的联系（这可以通过0.69的遗传指数体现出来）(Christian, JC, et al (1989))。这种与遗传学相对较高的联系被报道主要是用于解释下面的现象：黑种人的骨密度比白种人高10%，而白种人的骨密度大约比亚洲人高4%。正是与遗传学的这种强烈的关联性证明将个别的患者与其相似的参考群体进行比较是合理的。最终，大量文献证明，为被评估的患者建立与健康人群最相似的参考人群是很合理的，这也是为什么骨密度评估仪器制造商通常会提供与患者性别、年龄和种族背景相匹配的、有证明文件并经过验证的参考值来计算与患者有关的T值和Z值。

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