Evaluation of bioelectrical impedance analysis in measuring body fat in 6-to-12-year-old boys compared to air displacement plethysmography

Air displacement plethysmography (ADP) has been considered the ‘standard’ method to determine body fat in children due to superior validity and reliability compared to bioelectrical impedance analysis (BIA). However, ADP and BIA are used interchangeably despite few studies comparing measures of percentage body fat by ADP (%FMADP) with BIA (%FMBIA) in children with and without obesity. The objective of this study was to measure concurrent validity and reliability of %FMADP and %FMBIA in 6-to-12-year-old boys with and without obesity. Seventy-one boys (25 with obesity) underwent body composition assessment. Ten boys participated in intra-day reliability analysis. %FMADP was estimated by Bodpod using gender- and age-specific equations of body density. %FMBIA was estimated by a multi-frequency, hand-to-foot device using child-specific equations based on impendence. Validity was assessed by t-tests, correlation coefficients and limits of agreement (LoA); and reliability by technical error of measurement (TEM) and intraclass correlation coefficients (ICCs). Compared to %FMADP, %FMBIA was significantly underestimated in the cohort (-3.4 ± 5.6%; effect size = 0.42), and in both boys with obesity (-5.2 ± 5.5%; ES = 0.90) and without obesity (-2.4 ± 5.5%; ES = 0.52). A strong, significant positive correlation was found between %FMADP and %FMBIA (r = 0.80). Across the cohort, LoA were 22.3%, and no bias was detected. For reliability, TEM of 0.65% and 0.55%, and ICCs of 0.93 and 0.95 for %FMBIA and %FMADP respectively. Whilst both %FMADP and %FMBIA are highly reliable methods, considerable differences indicated that the devices cannot be used interchangeably in boys 6-to-12-years-old.