Comparison of two hologic DXA systems (QDR 1000 and QDR 4500/A) for in vivo bone mass measurement in the baboon (Papio ursinus)

Dual-energy X-ray absorptiometry (DXA) is the gold standard for bone mass measurement in humans. New generation osteodensitometers have been introduced and numerous studies have been performed to compare new and old devices for in vivo measurements of bone mineral density (BMD). However similar studies in nonhuman primates have yet to be performed. In this longitudinal study, two generation of osteodensitometers from the same manufacturer (Hologic QDR 1000 and Hologic QDR 4500/A) were used to detect bone changes in a cohort of 24 ovariectomized (OVX) Chacma baboons (Papio ursinus) during a period of 36 mo. Correlation between the same osteodensitometers were also obtained for the lumbar spine (L1-L4) area, BMD, and bone mineral content (BMC) in a cohort of 33 adult female baboons and for the total hip area, BMD, and BMC in a group of 25 adult female baboons. The QDR 1000 to QDR 4500/A area, BMC, and BMD correlation coefficient (r(2)) were 0.848, 0.939, and 0.916, respectively; r(2) for total hip BMD was 0.818. Percentage of variation (PV) among the total vertebral (L1-L4) area measured by the two osteodensitometers was 5.3 +/- 2.3 (mean +/- SD). BMC had the lowest PV and the highest r(2). The mean lumbar BMD was higher when measured by QDR 1000 with a PV% of 7.7 +/- 3.1 (mean +/- SD). The mean hip BMD was higher measured by QDR 1000 with a PV% of 9.3 +/- 7.1 (mean +/- SD). Slopes of two regression lines for the lumbar spine (L1-L4) and total hip BMD were 0.928 and 0.914, respectively. Longitudinal analysis of lumbar BMD in OVX baboons showed that QDR 4500/A detected a significant bone density increase at 36 and 48 mo post-OVX, compared to time 12, whereas the QDR 1000 did not. Our results indicate that both osteodensitometers can be used to measure bone changes in longitudinal studies in primates, but that before upgrading to a new-generation osteodensitometer, a calibration curve has to be obtained so that both devices can be equally used in regular experimental study in nonhuman primates.