In vivo quantification of fat content in mice using the Hologic QDR 4500A densitometer

Purpose: Validation of dual-energy X-ray absorptiometry (DXA) with the Hologic QDR 4500A (QDR 4500) Fan Beam X-ray densitometer for in vivo assessment of body fat content in mice. Methods: Precision of DXA fat measurement was assessed by repeated in vivo scanning and re-positioning of different sized mice (17.6, 24.6, 34.2 g). DXA fat and total mass measurements were correlated with dissected tissue weights in 240 female adult mice of seven strains (mean weights 21.9-26.8 g). Accuracy of DXA fat tissue measurements was assessed by chemical analysis in a subgroup of 40 female decapitated mice (mean weights 19.6-28.4 g). Results: Precision of the DXA measurements for fat mass was dependent on body weight (mean coefficient of variation, CV, 34.2 g mouse: 7.53 ± 0.13%; 24.6 g mouse: 32.16 ± 0.17%; 17.6 g mouse: 40.64 ± 0.06%). A moderate to high correlation with the dissected fat tissue weights was found for all seven strains: r = 0.52, p ≤ 0.01 (AJ) to r = 0.83, p ≤ 0.01 (CBA, both mean weight = 22 g). The correlation of DXA measurements with the chemical analysis of the carcass was good to excellent (r = 0.80, p ≤ 0.01). Conclusion: The results demonstrate that the QDR 4500A DXA can be utilised for in vivo measurements of fat content in mice weighing as little as 20 g, with excellent correlations between tissue dissections and chemical analysis demonstrating high consistency of the measurements. DXA values were consistently slightly lower than those by direct chemical analysis; however, the limits of agreement (mean difference 0.96 g) demonstrated good concordance between the two methods.