Bone mass assessment in rats by dual energy X-ray absorptiometry

At present there are many techniques available for determining bone mass, measurement of which is essential for monitoring osteopenia. Rats are preferred to other laboratory species when designing animal studies on osteoporosis. The precision and accuracy of dual energy X-ray absorptiometry (DXA) for the assessment of bone mineral density (BMD) and bone mineral content (BMC) in laboratory animals were assessed. Precision, expressed as a coefficient of variation (CV), was measured, making five determinations (Hologic QDR-1000) on lumbar spine (in vivo) and femur (in vitro), both with and without repositioning. The correlation (r) between densitometric parameters and mineral content of bone ashes was calculated both in lumbar spine (in vivo) and in femur (in vitro). In our study, DXA had good precision, better in femur (CV 0.53%) than in lumbar spine (L2-L4) (CV 1.0%). Repositioning did not increase significantly the coefficients of variation (CV 0.61% and 1.2%, respectively). The linear regression between BMD and ash weight, calcium and phosphorous content showed high correlation coefficients (r = 0.64-0.85, p < 0.05). Although we found an overestimate of values of BMC with respect to ash weight (21% in lumbar spine and 31% in femur), the correlation between BMC and mineral content was high (r = 0.96-0.99, p < 0.05). The results suggest that the DXA technique has the precision necessary when used to assess BMD and BMC in small laboratory animals.