Related Experiment Video
Updated: Jul 20, 2025
Evaluation of Fluid Overload by Bioelectrical Impedance Vectorial Analysis
Published on: August 17, 2022
Prediction of fat-free mass in young children using bioelectrical impedance spectroscopy
Jaz Lyons-Reid1, Leigh C Ward2, José G B Derraik1,3,4,5
1Liggins Institute, University of Auckland, Auckland, New Zealand.
Insights
A new bioimpedance equation accurately predicts fat-free mass (FFM) in 3.5-year-old children. This validated tool offers practical body composition assessment for preschoolers, though external validation is still needed.
Area of Science:
- Pediatric Nutrition and Body Composition
- Biomedical Engineering and Measurement Science
Background:
- Bioimpedance devices offer practical body composition analysis for preschool children.
- Current limitations exist due to a lack of validated predictive equations for this age group.
Purpose of the Study:
- To develop and validate novel fat-free mass (FFM) prediction equations using bioimpedance analysis.
- To establish dual-energy X-ray absorptiometry (DXA) as the reference standard for validation.
- To specifically target New Zealand 3.5-year-old children.
Main Methods:
- Bioelectrical impedance spectroscopy (SFB7) and DXA (iDXA) measurements were performed on 65 children.
- A predictive equation was developed incorporating weight, sex, ethnicity, and impedance (resistance at 50 kHz).
- The new equation's performance was compared against published equations and mixture theory predictions.
Main Results:
- The developed equation explained 88% of FFM variance, with a root mean squared error of 0.39 kg (3.4% of mean FFM).
- Internal validation showed minimal bias (40 g) and limits of agreement of ±7.6% of mean FFM.
- Published equations exhibited significant bias when validated in this cohort, while the SFB7 inbuilt equation with personalized geometry showed larger bias and LOA compared to the empirical equation.
Conclusions:
- A novel bioimpedance equation for predicting FFM in 3.5-year-old children has been successfully developed and validated.
- The developed equation demonstrates high accuracy and minimal bias, making it a promising tool for pediatric body composition assessment.
- Further external validation is recommended to confirm the generalizability and reliability of the new bioimpedance equation across diverse populations.
Background:
Bioimpedance devices are practical for measuring body composition in preschool children, but their application is limited by the lack of validated equations.
Objectives:
To develop and validate fat-free mass (FFM) bioimpedance prediction equations among New Zealand 3.5-year olds, with dual-energy X-ray absorptiometry (DXA) as the reference method.
Methods:
Bioelectrical impedance spectroscopy (SFB7, ImpediMed) and DXA (iDXA, GE Lunar) measurements were conducted on 65 children. An equation incorporating weight, sex, ethnicity, and impedance was developed and validated. Performance was compared with published equations and mixture theory prediction.
Results:
The equation developed in ~70% (n = 45) of the population (FFM [kg] = 1.39 + 0.30 weight [kg] + 0.39 length2/resistance at 50 kHz [cm2/Ω] + 0.30 sex [M = 1/F = 0] + 0.28 ethnicity [1 = Asian/0 = non-Asian]) explained 88% of the variance in FFM and predicted FFM with a root mean squared error of 0.39 kg (3.4% of mean FFM). When internally validated (n = 20), bias was small (40 g, 0.3% of mean FFM), with limits of agreement (LOA) ±7.6% of mean FFM (95% LOA: -0.82, 0.90 kg). Published equations evaluated had similar LOA, but with marked bias (>12.5% of mean FFM) when validated in our cohort, likely due to DXA differences. Of mixture theory methods assessed, the SFB7 inbuilt equation with personalized body geometry values performed best. However, bias and LOA were larger than with the empirical equations (-0.43 kg [95% LOA: -1.65, 0.79], p < 0.001).
Conclusions:
We developed and validated a bioimpedance equation that can accurately predict FFM. Further external validation of the equation is required.
