Submitted to: Journal of Clinical Densitometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2007
Publication Date: 12/1/2007
Citation: Shypailo, R.J., Ellis, K.J. 2005. Bone assessment in children: Comparison of fan-beam dxa analysis. Journal of Clinical Densitometry. 4(8):445-453 Interpretive Summary: Dual-energy X-ray absorptiometry (DXA) is used in body composition research for measuring bone density (BMD) and bone mineral content (BMC). Apparent inaccuracies in measuring whole-body bone in small subjects have led to the development of a new version of analysis software (version 12.1) by Hologic, the manufacturer of the DXA instruments used in our facility. The new software uses weight to correct scans of subjects weighing less than 40 kg. We used the new software to re-analyze over 1100 scans of both boys and girls, from 2 to 18 years old, previously analyzed by our original software (version 11.2). We applied several statistical tests to the results, and compared the old and new results with age, weight, and height. Statistical regression analysis showed that the two versions of analysis software are highly correlated; however, trend lines did not lie on the 1-to-1 line. BMC was increased in smaller subjects, while BMD was lowered. The differences diminished with increasing body weight, approaching zero at about 40 kg. Original and new results were in agreement by about age 14 yrs in both boys and girls. The greatest changes were seen in the legs, followed by the arms and torso. The head was not affected. The new software was found to produce significant changes in whole-body bone values for subjects weighing less than 40 kg, when compared to earlier versions. The effect was greater at smaller body weights. These results will have an impact on longitudinal DXA studies in children, and on existing normal reference databases for pediatric whole-body bone values. Investigators must be aware of what software version is used by their DXA instruments, and what software version was used to produce any reference database they may use for comparison.
Technical Abstract: The newest version of whole-body DXA analysis software from Hologic (Discovery 12.1) is designed to enhance bone detection in smaller subjects. We re-analyzed 1127 pediatric scans (ages 1.8-18.5 yr) previously analyzed using version 11.2. Regression analysis compared new and original results for bone area (BA), bone mineral content (BMC), bone density (BMD), and DXA weight. Changes in total and regional bone results were compared with age, weight, and height. New results were highly correlated with original analyses (R squared greater than/equal to 0.9). The BA and BMC values increased in subjects less than 40 kg in weight, resulting in a lower BMD. Original and new results were equivalent by about age 14 yr in both genders. Regional bone data showed the greatest changes in the legs; the head was relatively unaffected. The newest software produces significant changes in bone values in subjects weighing less than 40 kg, compared to earlier versions. The effect increases with decreasing body weight. This will impact interpretation of longitudinal pediatric DXA studies, as well as existing pediatric whole-body bone reference databases. Investigators must recognize which DXA software version they are using, and which version produced any reference database they may use for comparison.