Precision of high-resolution dual energy X-ray absorptiometry of bone mineral status and body composition in small animal models.

The purpose of this study was to analyze the in situ precision (reproducibility) of bone mineral and body composition measurements in mice of different body weights and rats, using a high-resolution DXA (dual energy X-ray absorptiometry) scanner. We examined 48 NMRI mice weighing approximately 10 to 60 g, and 10 rats weighing approximately 140 g. Four repeated measurements were obtained on different days. In mice, the standard deviations of repeated measurements ranged from 2.5 to 242 mg for bone mineral content (BMC), from 0.16 to 3.74 g for fat, and from 0.40 to 4.21 g for lean mass. The coefficient of variation in percent (CV%) for BMC/BMD (bone mineral density) was highest in the 10 g mice (12.8% / 4.9%) and lowest in the 40 g mice (3.5% /1.7%). In rats, it was 2.5 /1.2% in the lower extremity, 7.1/3.0 % in the spine, 5.7/2.0 % in the femur, and 3.6%/2.1% in the tibia. The CV% for fat and lean mass in mice was higher than for BMC. The study demonstrates good precision of bone mineral and moderate precision of body composition measurements in small animals, using a high-resolution DXA system. The technique can be used for testing the efficacy of drugs in small animal models, for mutagenesis screens, and for the phenotypic characterization of transgenic mice.