Comparison of four bioelectrical impedance analysis formulas in healthy elderly subjects

Background: Changes of body composition occur with aging and influence heal th status. Thus accurate methods for measuring fat-free mass (FFM) in the e lderly are essential. Objective: The purpose of this study was to compare F FM obtained by three bioelectrical impedance analysis (BIA) published formu las specific for the elderly and one equation intended for all age groups, with FFM derived from dual-energy X-ray absorptiometry (FFMDXA), in healthy elderly subjects. Methods: Healthy Caucasian subjects over 65 years (106 w omen, age 75 +/- 6.2, body mass index 25.2 +/- 4.1 and 100 men, age 74.6 +/ - 6.6, body mass index 25.8 +/- 3.0) were measured by DXA (Hologic QDR-4500 ) and BIA (Xitron, 50 kHz). FFMBIA was calculated by the published formulas of Deurenberg, Baumgartner, Roubenoff and Kyle and compared to FFMDXA by a Bland-Altman analysis. Results: The Deurenberg and Roubenoff BIA formulas underestimated FFM compared to DXA by -7.1 and -2.9 kg in women and -6.7 an d -2.3 kg in men, respectively. The Baumgartner formula overestimated FFM b y 4.3 kg in women and 1.4 kg in men. The Kyle formula showed differences of 0.0 kg in women and 0.2 kg in men, and the limits of agreement of FFMBIA ( Kyle) relative to FFMDXA were -3.3 and +3.3 kg for women and -3.8 and +4.3 kg for men. Conclusion: The Kyle BIA formula accurately predicts FFM in eld erly Swiss subjects between 65 and 94 years, with a body mass index of 17 t o 34.9 kg/m(2). The other BIA formulas developed especially for the elderly are not valid in this population. Copyright (C) 2001 S. Karger AG, Basel.