The Evaluation of Consistency Between Body Composition Assessments in Pediatric Population Using Pencil Beam and Fan Beam Dual-Energy X-Ray Absorptiometers

The replacement of the old dual-energy X-ray absorptiometry system with a novel one should be preceded by a cross-calibration procedure. Therefore, the study was aimed at investigating the consistency of bone and body composition measures performed in pediatric population using pencil beam (DPX-L; GE Healthcare, GE Healthcare, Madison, WI) and fan beam (Prodigy; GE Healthcare, GE Healthcare, Madison, WI) densitometers. The study group consisted of 212 healthy children aged 4-18 yr. Total body (TB) and lumbar spine (S) (L2-L4) measurements were performed using DPX-L and Prodigy during the same visit. Bland-Altman analysis, linear regressions, and paired t-test were performed to evaluate the consistency of measurements and to establish a cross-calibration equation. The average Prodigy values for TB and lumbar spine bone mineral density (BMD) and content (BMC) were 2.7%, 2.4% and 1.6%, 1.6% higher than those of DPX-L, respectively (p < 0.0001). Prodigy-assessed bone area (BA) was lower by 1.4% for TBBA (p < 0.0001) and 1.1% for SBA (p < 0.001). Lean body mass (LBM) from Prodigy was higher by 6.9% (p < 0.0001), whereas fat mass (FM) was lower by 8.4% compared with those from DPX-L (p < 0.0001). Bland-Altman analyses revealed the effect of magnitude that was nonlinear (2nd degree polynomial) for TBBMD (r = 0.32, p = 0.001), TBBMC (r = 0.51, p < 0.0001), TBBA (r = 0.34, p < 0.0001), and LBM (r = 0.56, p < 0.0001), but not for FM (r = 0.14, not significant [n.s.]). In contrast, in lumbar spine, the magnitude dependence was linear and significant for SBMC (r = 0.46, p < 0.0001) and SBA (r = 0.34, p < 0.0001) but not for SBMD (r = 0.12, n.s.). Both skeletal and body composition variables assessed by DPX-L and Prodigy devices were highly correlated, showing R2 values ranging from 0.976 for FM to 0.994 for SBMC. The results of this study document a necessity for implementation of calculated cross-calibration equations to transform DPX-L-based local pediatric references into a novel Prodigy system.