Use of Bioelectrical Impedance Analysis and Anthropometry to Measure Fat-free Mass in Children and Adolescents With Crohn Disease
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ABSTRACTObjectives:To investigate the precision of published prediction equations for fat‐free mass (FFM) from bioimpedance measurements in children with Crohn disease using dual‐energy X‐ray absorptiometry (DXA) as an in vivo gold standard.Methods:Fat‐free mass of 49 white boys and girls ages 7.3 to 16.9 y suffering from Crohn disease was measured by DXA. Body weight, height and bioimpedance measurements were also collected. FFM measured by DXA (FFMDXA) was compared with FFM predicted by the only 5 published prediction equations available for children and adolescents. An equation was developed for predicting FFM and was validated using a bootstrap method.Results:When correlating predicted FFM with FFMDXA, Schaefer's equation showed the highest R2 (0.950), the smallest standard error of estimate (SEE) (2.05 kg) and the smallest percentage error (0.28%). Our prediction equation for estimating FFM was FFM = 0.652 Ht2/Z + 0.0385 Wt + 0.586 Age − 0.327, R2 = 0.951, SEE = 2.08, P < 0.0005, where Ht2/Z is the impedance index in cm2/Ω, Wt is body weight in kilograms, age is in years. R2 value from bootstrap method was 0.950 ± 0.01 (95% confidence interval 0.927–0.968), indicating an acceptable validation of the derived formula.Conclusions:The formula of Schaefer is the best for predicting FFM. The present study provides a new prediction equation for estimating FFM in children with Crohn disease that may be used in clinical settings in which more sophisticated body composition measuring equipments are not available.
