The Validity of Bioelectrical Impedance Analysis to Measure Body Composition in Phenylketonuria.

ABSTRACT

AIM: To compare the measurement of total body water (TBW) and fat-free mass (FFM) using the criterion method of deuterium dilution space (2H2O) with bioelectrical impedance analysis (BIA) using a portable QuadScan 4000, Bodystat® in children and adolescents with phenylketonuria (PKU). METHODS: Sixteen patients with PKU, median age is 12.5 (range 5-20.6) years, were recruited into this cross-sectional study. TBW was measured by both deuterium dilution and BIA on the same occasion as per a standard protocol. FFM was estimated from predictive equations. RESULTS: There was no significant difference between TBWDeut and TBWBIA (p = 0.344) or FFMDeut and FFMBIA (p = 0.111). TBWDeut and TBWBIA were highly correlated (r = 0.990, p < 0.0001), as were FFMDeut and FFMBIA (r = 0.984, p < 0.0001). Bland-Altman plots demonstrated that there was no proportional bias between the criterion method, TBWDeut, and the test method TBWBIA, in estimating TBW (ß = -0.056, adjusted r 2 = 0.069, p = 0.169) or FFM (ß = -0.089, adjusted r 2 = 0.142, p = 0.083). CONCLUSION: Our results suggest that when compared with the criterion method, the QuadScan 4000, Bodystat® can reliably be used to predict TBW and FFM in patients with PKU. We suggest that due to the portability and non-invasive approach, this method can reliably be used to monitor body composition in the outpatient clinic setting, to further improve the monitoring and assessment of nutritional status in PKU.