Within- and between-laboratory precision in the measurement of body volume using air displacement plethysmography and its effect on body composition assessment

Abstract

OBJECTIVE:To determine and compare the extent of within-and between-laboratory precision in body volume (BV) measurements using air displacement plethysmography (ADP), the BOD POD body composition system, and to interpret any such variability in terms of body composition estimates. DESIGN: Repeated test procedures of BV assessment using the BOD POD ADP were reproduced at two laboratories for the estimation of precision, both within and between laboratories. SUBJECTS: In total, 30 healthy adult volunteers, 14 men (age, 19-48 y; body mass index (BMI), 19.7-30.3 kg/m 2 ) and 16 women (age, BMI,.7 kg/m 2 ), were each subjected to two test procedures at both laboratories. Two additional volunteers were independently subjected to 10 repeated test procedures at both laboratories. MEASUREMENTS: Repeated measurements of BV, uncorrected for the effects of isothermal air in the lungs and the surface area artifact, were obtained using the BOD POD ADP, with the identical protocol being faithfully applied at both laboratories. Uncorrected BV measurements were adjusted to give estimates of actual BV that were used to calculate body density (body weight (BWt)/actual BV) from which estimates of body composition were derived. The differences between repeated BV measurements or body composition estimates were used to assess within-laboratory precision (repeatability), as standard deviation (SD) and coefficient of variation; the differences between measurements reproduced at each laboratory were used to determine between-laboratory precision (reproducibility), as bias and 95% limits of agreement (from SD of the differences between laboratories). RESULTS: The extent of within-laboratory methodological precision for BV (uncorrected and actual) was variable according to subject, sample group and laboratory conditions (range of SD, 0.04-0.13 l), and was mostly due to within-individual biological variability (typically 78-99%) rather than to technical imprecision. There was a significant (Po0.05) bias between laboratories for the 10 repeats on the two independent subjects (up to 0.29 l). Although no significant bias (P ¼ 0.077) was evident for the sample group of 30 volunteers (À0.05 l), the 95% limits of agreement were considerable (À0.68 to 0.58 l). The effects of this variability in BV on body composition were relatively greater: for example, within-laboratory precision (SD) for body fat as % BWt was between 0.56 and 1.34% depending on the subject and laboratory; the bias (À0.59%) was not significant between laboratories, but there were large 95% limits of agreement (À3.67 to 2.50%). CONCLUSION: Within-laboratory precision for each BOD POD instrument was reasonably good, but was variable according to the prevailing conditions. Although the bias between the two instruments was not significant for the BV measurements, implying that they can be used interchangeably for groups of similar subjects, the relatively large 95% limits of agreement indicate that greater consideration may be needed for assessing individuals with different ADP in...

Interdevice variability in percent fat estimates using the BOD POD

“…In a similar study to the present, Collins et al (2004) found that the interdevice reliability between BP units in separate laboratories was acceptable. However, the study observed relatively large 95% limits of agreement (À3.7 to 2.5 %BF), indicating that practitioners should heed caution when using two different units.…”

“…In the current study, we found that the agreement in measured TGV values between the two BP units (r 2 ¼ 0.98, Po0.001) was as good as the agreement in repeated measurements of TGV by a single BP (r 2 ¼ 0.95, Po0.001) (Collins & McCarthy, 2003). In order to make a direct comparison in interdevice reliability with that from Collins et al (2004), we reassessed interdevice reliability by comparing %BF estimates from the two BP units using predicted TGV. The agreement in %BF estimates between the two BP units, in terms of mean difference (0.571.2 %BF), 95% limits of agreements (À1.9-2.9 %BF) and within-subject CV (3.172.2%), was found to be better than that observed by Collins et al (2004), and was similar to that calculated using measured TGV in this study.…”

“…However, the study observed relatively large 95% limits of agreement (À3.7 to 2.5 %BF), indicating that practitioners should heed caution when using two different units. Collins et al (2004) pointed out that some of their observed difference between units could be due to environmental differences between laboratories and/or the effects of time between tests, not necessarily differences between the BP units themselves. The current study is unique in that we controlled for these factors by placing two identical units in the same room under the exact same environmental conditions and by completing successive tests (same subject) within 5 min of each other.…”

“…The current study is also distinct in that TGV was measured. Collins et al (2004) used a predicted value for TGV, resulting in a constant value between both BP units. TGV is a factor in the calculation of Db:…”

“…Although intradevice reliability has been evaluated for the BP, interdevice reliability is virtually unknown. In the only relevant study, Collins et al (2004) compared between-laboratory precision of body volume via the BP, however, this analysis included biological and environmental variability due to transportation time between the laboratories, rendering the variability of the actual device to be undefined. Interdevice reliability is crucial for determining overall validity and has practical implications for multicenter studies, intersite testing and acceptance as a reference method for body composition.…”