Body Composition Measurement in Bronchiectasis: Comparison between Bioelectrical Impedance Analysis, Skinfold Thickness Measurement, and Dual-Energy X-ray Absorptiometry before and after Pulmonary Rehabilitation.

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/m) >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.