Comparison of Hologic QDR‐1000/W and 4500W DXA Scanners in 13‐ to 18‐Year Olds

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Abstract
Objective: Body composition measurements made using Hologic QDR‐1000/W pencil‐beam and QDR‐4500W fan‐beam scanners (Bedford, MA) were compared in a sample of 13‐ to 18‐year‐old white and black youth (n = 219). Research Methods and Procedures: Total fat (FAT), fat‐free soft tissue (FFST), bone mineral content (BMC), bone mineral density (BMD), and percent body fat (%BF) were compared between repeated measurements using the QDR‐4500 and between the two scanners using mixed model ANOVA. Intraclass correlation coefficients and Bland‐Altman limits of agreement were used to evaluate inter‐ and intrascanner reliability. Results: Intraclass correlation coefficients for repeated measurements using the QDR‐4500 ranged from 0.997 to 0.999 for FAT, %BF, FFST, and BMC and 0.987 for BMD. Mean measurements made using the two scanners differed significantly for FAT, %BF, BMC, and BMD (p < 0.0001), and scan by sex interactions were significant (all p < 0.0005). There were no significant differences in mean measurements between repeat scans using the QDR‐4500 (all p > 0.19). Limits of agreement for measurements of FAT, FFST, and %BF made using the two scanners were approximately three times as wide as those for two measurements using the QDR‐4500. For lower values of FAT and %BF, the QDR‐4500 gave higher measurements than the QDR‐1000, whereas at higher values, this relationship was reversed. The QDR‐1000 tended to give higher BMC measurements, with larger differences for higher values. Discussion: Using different models of DXA scanners within a study may reduce precision of body composition measurement. This issue needs to be considered in the design of longitudinal studies.