Dual energy X-ray absorptiometry in small rats with low bone mineral density

The feasibility of dual energy X-ray absorptiometry (DXA) using the Norland XR-26 Mark II bone densitometer for measurements of bone mineral content ( BMC) and bone mineral density (BMD) in small rats was evaluated. Thirty-two young, isogenic, Lewis rats (weights from 119 g to 227 g) were used, norma l rats (n = 7) and rats with low BMD obtained from three different vitamin D-depleted models (n = 25). DXA measurements were performed using the speci al software for small animals. Duplicate scans of excised femurs performed at 2 mm/second (pixel size of 0.5 mm x 0.5 mm) were very precise measuremen ts with a coefficient of variation (CV) below 1.6% in animals with normal B MD; in rats with low BMD, the CV was significantly higher (P = 0.02-0.04), 7.8% and 4.4% for BMC and BMD, respectively. Regression analysis demonstrat ed that these measurements were related to the ash weight (R-2 > 98.6%). Th e CV for measurements of the lumbar spine at 10 mm/second (pixel size 0.5 m m x 0.5 mm) was 2.6% and 2.2%: for BMC and BMD, respectively in rats with n ormal BMD. and again higher (P = 0.03-0.14) in rats with low BMD, 7.3% and 4.7%, respectively, for BMC and BMD. Even though low CVs were obtained for total body duplicate scans (scan speed of 20 mm/second and a pixel size of 1.5 mm x 1.5 mm). the measurements were problematic for accuracy because of an overestimation of both BMC and the area of bone, Using these scan param eters the measurements of total body bone mineral could not be recommended in small rats with low BMD.