Assessment of Body Composition of Rats by Bioimpedance Spectroscopy: Validation Against Dual-Energy X-Ray Absorptiometry
Fat-free mass (FFM) and fat mass (FM) were determined in male and female out-bred Wistar strain rats by both dual-energy X-ray absorptiometry (DXA) and by bioimpedance spectroscopy (BIS). Data obtained by both methods were highly correlated and exhibited a small (4%) bias for FFM, with relatively small limits of agreement (approximately ± 10%), but differed to a much larger degree for FM (14 to 27% bias), with wide limits of agreement (± 50%). Inter-method correction equations are provided to allow conversion of data from one method to another, eliminating bias, but not altering the limits of agreement. Since both methods exhibited a high degree of precision of measurement, it is suggested that the poor agreement for measurement of fat mass is a reflection that fat mass is an indirectly-derived value, which includes unavoidable propagation of prediction errors associated with the primary measures. Both BIS and DXA provide rapid, minimally invasive and, in the case of BIS, portable techniques for body composition analysis. Their use for estimation of FFM may be recommended, but, for prediction of fat mass, exercise of caution would be prudent.