Precise measurement of bone mineral density in rats using dual-energy X-ray absorptiometry

The dual X-ray absorptiometer (DEXA, Hologic ZDR-1000) in a high resolution mode was evaluated for measuring: Area (A), Bone Mineral Content (BMC) and Bone Mineral Density (BMD) in femur and tibia of adults rats at four regions: proximal (L1), diaphysis (L2-L3) and distal (L4). Reproducibility with and without repositioning was evaluated in femur after ten measurements in a water bath at depths between 2.0 and 2.5 cm. The whole coefficient of variation (CV = 100 x SD/mean) of BMD was 0.52% and 0.47% respectively. Accuracy was evaluated by comparing the BMC to bone ash weight. BMC was highly correlated with chemical analysis (r = 0.98, p < 0.001) for femur. The ability to detect changes in BMD was studied by comparing BMD of the right and left femurs and tibias of adult normal males and females rats. No significant differences were found between both sides. Nevertheless, when BMD (X +/- SE) of male and female rats were compared, female rats presented lower BMD at distal femur (0.263 +/- 0.021 vs. 0.315 +/- 0.009, p < 0.05) and proximal tibia (0.259 +/- 0.016 vs. 0.315 +/- 0.013 p < 0.02) than male rats. We also studied the ability to detect BMD changes in abnormal metabolic conditions. SHAM operated rats were compared to ovariectomized (OVX) rats and it was observed that femur of OVX showed a lower distal BMD than SHAM (0.217 +/- 0.005 vs. 0.263 +/- 0.021, p < 0.05). In summary, DEXA is a technique accurate and precise enough to detect changes on BMC and BMD in small animals permitting the experimental study of different metabolic bone conditions.