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

Air displacement plethysmography (ADP) has been considered as the 'standard' method to determine body fat in children due to superior validity and reliability compared with bioelectrical impedance analysis (BIA). However, ADP and BIA are often 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 (twenty-five with obesity) underwent body composition assessment. Ten boys participated in intra-day reliability analysis. %FMADP was estimated by Bodpod using sex- and age-specific equations of body density. %FMBIA was estimated by a multi-frequency, hand-to-foot device using child-specific equations based on impedance. 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 (ICC). Compared with %FMADP, %FMBIA was significantly underestimated in the cohort (-3 center dot 4 +/- 5 center dot 6 %; effect size = 0 center dot 42) and in both boys with obesity (-5 center dot 2 +/- 5 center dot 5 %; ES = 0 center dot 90) and without obesity (-2 center dot 4 +/- 5 center dot 5 %; ES = 0 center dot 52). A strong, significant positive correlation was found between %FMADP and %FMBIA (r = 0 center dot 80). Across the cohort, LoA were 22 center dot 3 %, and no proportional bias was detected. For reliability, TEM were 0 center dot 65 % and 0 center dot 55 %, and ICC were 0 center dot 93 and 0 center dot 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 age 6-to-12 years.