BACKGROUND In individuals with bronchiectasis, fat-free mass depletion may be common despite a low prevalence of underweight and is considered a risk factor for increased morbidity and mortality. Techniques to adequately estimate fat-free mass and its changes over time are needed. OBJECTIVE The purpose of this study was to assess agreement among values obtained with three different body composition techniques: skinfold thickness measurement (STM), bioelectrical impedance analysis (BIA), and dual-energy x-ray absorptiometry (DXA). DESIGN The study was a secondary analysis of data from a randomized controlled trial. PARTICIPANTS/SETTING A respiratory rehabilitation program was administered for 3 months to individuals with bronchiectasis from the bronchiectasis unit of the Regional University Hospital in Malaga, Spain, from September 2013 to September 2014. Individuals with a body mass index (calculated as kg/m2) >18.5 who were aged 65 years or younger and those with a body mass index >20 who were older than 65 years were included. MAIN OUTCOME MEASURES At baseline and at 3 and 6 months, body composition was determined by DXA and STM. STATISTICAL ANALYSES PERFORMED Statistical concordance was assessed with the intraclass correlation coefficient (ICC), kappa coefficient, and the degree of agreement using the Bland Altman method. For comparison of the quantitative variables at baseline vs at 3 months and 6 months, the paired sample t test (or the Wilcoxon test) was used. RESULTS Thirty participants were included. Strong agreement was observed between body composition values determined by BIA and DXA in fat mass (ICC: 0.92) and fat-free mass (ICC: 0.87). Strong agreement was observed between STM and DXA in the values for fat-free mass (ICC: 0.91) and fat mass (ICC: 0.94), and lower agreement was observed for the longitudinal data and in the regional values. The mean difference between fat-free mass determined by BIA and DXA was + 4.7 with a standard deviation of 2.4 kg in favor of BIA. The mean difference between fat-free mass determined by STM and DXA was +2.3 with a standard deviation of 2.7 kg in favor of STM. Six individuals were classified as having a low fat-free mass index (20%) by DXA vs four by STM (13%; kappa: 0.76) and only two by BIA (6.6%; kappa: 0.44) compared with DXA. CONCLUSIONS Despite good statistical agreement among values obtained with DXA, STM, and BIA, the study findings indicate that STM and BIA, above all, tended to overestimate fat-free mass compared with DXA.

中文翻译：

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支气管扩张的身体成分测量：肺康复前后生物电阻抗分析、皮褶厚度测量和双能 X 射线吸收测定法的比较

背景 在患有支气管扩张症的个体中，尽管体重不足的发生率较低，但无脂肪质量消耗可能很常见，并且被认为是发病率和死亡率增加的危险因素。需要充分估计无脂肪质量及其随时间变化的技术。目的 本研究的目的是评估使用三种不同身体成分技术获得的值之间的一致性：皮褶厚度测量 (STM)、生物电阻抗分析 (BIA) 和双能 X 射线吸收测定法 (DXA)。设计 该研究是对随机对照试验数据的二次分析。参与者/环境 西班牙马拉加地区大学医院支气管扩张病房的支气管扩张患者接受了为期 3 个月的呼吸康复计划，2013 年 9 月至 2014 年 9 月。 体重指数（以 kg/m2 计算）>18.5 且年龄在 65 岁及以下的个体和体重指数>20 且年龄大于 65 岁的个体被纳入。主要结局指标在基线和 3 个月和 6 个月时，通过 DXA 和 STM 确定身体成分。执行的统计分析 使用 Bland Altman 方法通过组内相关系数 (ICC)、kappa 系数和一致性程度评估统计一致性。为了比较基线与 3 个月和 6 个月的定量变量，使用配对样本 t 检验（或 Wilcoxon 检验）。结果 包括三十名参与者。通过 BIA 和 DXA 测定的脂肪量（ICC：0.92）和无脂肪量（ICC：0.87）的身体成分值之间观察到很强的一致性。STM 和 DXA 在无脂肪质量 (ICC: 0.91) 和脂肪质量 (ICC: 0.94) 值方面观察到很强的一致性，纵向数据和区域值的一致性较低。由 BIA 和 DXA 确定的无脂肪质量之间的平均差异为 + 4.7，标准偏差为 2.4 kg，有利于 BIA。STM 和 DXA 测定的无脂肪质量之间的平均差异为 +2.3，标准偏差为 2.7 kg，有利于 STM。与 DXA 相比，DXA 将 6 个人归类为无脂肪质量指数低 (20%)，STM 归类为 4 人 (13%；kappa：0.76)，BIA 归类为仅 2 人 (6.6%；kappa：0.44)。结论 尽管使用 DXA、STM 和 BIA 获得的值之间具有良好的统计一致性，但研究结果表明，与 DXA 相比，STM 和 BIA 最重要的是倾向于高估无脂肪质量。