Does standardized BMD still remove differences between Hologic and GE-Lunar state-of-the-art DXA systems?

The standardized bone mineral density (sBMD) values, derived using universal standardized equations, were shown to be equivalent within 1.0% for hip but significantly different for spine for state-of-art fan-beam dual X-ray absorptiometry (DXA) Hologic and GE-Lunar systems. Spine L1-L4 and L2-L4 sBMD mean differences between the two systems were 0.042 g/cm(2) (4.1%) and 0.035 g/cm(2) (3.2%), respectively.

The objective of this study is to validate the 1994 pencil-beam DXA "universal standardization equations" for state-of-the-art fan-beam DXA systems.

The spine and bilateral femurs of 87 postmenopausal women were scanned on both Hologic Delphi and GE-Lunar Prodigy DXA systems at three different clinical centers. The scans were analyzed using Hologic Apex and GE-Lunar EnCore software. The BMD results were converted to sBMD using the equations previously developed. Linear regression analysis was used to describe the relationship of the two systems' BMD results. Bland-Altman analysis was used to assess the differences in measures.

The Apex and Prodigy sBMD values were highly correlated (r ranged from 0.92 to 0.98). Spine L1-L4 and L2-L4 sBMD values had significant intercepts and slopes for Bland-Altman regression, with mean differences of 0.042 g/cm(2) (4.1%) and 0.035 g/cm(2) (3.2%), respectively. The total hip and neck sBMD showed no significant intercept and slope, except left total sBMD had a significant difference between the two systems of 0.009 g/cm(2) (1.0%).

The sBMD values were shown to be equivalent within 1.0% for hip but were significantly different for spine on the two systems. Biases may persist in pooled sBMD data from different manufacturers, and further study is necessary to determine the cause.