iDXA, Prodigy, and DPXL Dual-Energy X-ray Absorptiometry Whole-Body Scans: A Cross-Calibration Study

Purpose: Total body fat. lean, and bone mineral content (BMC) in addition to regional fat and lean mass values for arms, leas. and trunk were compared across a pencil-beam (Lunar DPXL) and 2 fan-beam (GE Lunar Prodigy and GE Lunar iDXA) dual-energy X-ray absorptiometry (DXA) systems. Methods: Subjects were a multiethnic sample of 99 healthy adult males (47%) and females (mean +/- SD: age. 46.3 +/- 16.9 yr; weight, 73.4 +/- 16.6 kg; height, 167.6 +/- 9.7 cm; body mass index, 26.0 +/- 5.2 kg/m(2)) who had whole-body scans performed within a 3-h period on the 3 systems. Repeated measures ANOVA was used to test the null hypothesis that the mean values for the 3 systems were equal. Translation equations between the methods were derived using regression techniques. Results: Bone mineral content (BMC): For both Genders. total BMC by iDXA was lower (p <= 0.004) than the other systems. Lean: for males, iDXA was lower (p <= 0.03) than the other systems for total, trunk, and arms. For females, DPXL estimated higher (p < 0.001) lean mass compared with the other systems for total, trunk, and arms. but iDXA estimated greater leas lean mass. For both Lenders. all DPXL mean values were greater than Prodigy mean values (p < 0.001). Fat: in females, all the 3 systems were different from each other for total, trunk, and legs (p <= 0.04). For arms. DPXL and iDXA were higher than Prodigy (p < 0.0004). For males, DPXL was less (p < 0.001) for total body. trunk. and leas compared with the other 2 systems and greater than Prodigy only for arms (p < 0.0007). These data were used to derive translation equations between systems. For several measurements, the differences between systems were related to gender. Conclusion: For stimation of BMC and body composition. there was high agreement between all DXA systems (R-2 = 0.85-0.99). Even so, cross-calibration equations should be used to examine data across systems to avoid erroneous conclusions.