Abstract
Different dual-energy x-ray absorptiometry (DXA) hardware can affect bone mineral density (BMD) measurements and different reference populations can affect t-scores. Long-term analyses describing differences in the relationship between BMD and t-scores are lacking. BMD-values were plotted against t-scores for 241 Lunar DXA scans on females obtained over 18 years from several centers in Sweden and Norway. The result of the plot was compared to hardware/software versions, reference populations and different software analysis settings (Basic vs Enhanced analysis for total body and Single Photon Absorptiometry (SPA) vs Lunar calibration for forearm). For the forearm compartments, we found different BMD-t-score relationships depending on the use of SPA or Lunar calibration (p<0.001). With Lunar calibration, BMD-values were 24% higher, but there was no effect on t-scores. Total body measurements with iDXA scanners and Enhanced analysis for Prodigy scanners (software version 14.10) resulted in a different BMD-t-score relationship compared to the other hardware/software versions (p<0.001), with the largest discrepancy for lower BMD-values. Switching from Basic to Enhanced analysis generally decreased BMD-values and often changed t-scores (both increased and decreased). For the femoral neck, there were two different BMD-t-score relationships caused by different reference populations (p<0.001). In contrast to total body, the difference for femoral neck was more pronounced for higher values, with little impact in the clinical decision-making area. Hardware, software, reference populations and software analysis settings can affect the BMD-t-score relationship, but do so differently for different compartments. The BMD-t-score-plot is a simple and effective tool to discover systematic differences. Longitudinal analyses of DXA scans should be performed based on raw data analyzed in “one run” with the same software version and settings, in order to avoid systematic differences.
Highlights
Measurement of bone mass by dual-energy x-ray absorptiometry (DXA) revolutionized the bone densitometry field, and improved standard care of patients with osteoporosis, when introduced more than 30 years ago [1, 2]
We demonstrate how the relationship between bone mineral density (BMD) and t-score can vary between different hardware/software versions, reference populations and different software analysis settings
We introduced the BMD-t-score-plot as a simple, but effective tool to identify random and systematic differences affecting the relationship between BMD and t-score
Summary
Measurement of bone mass by dual-energy x-ray absorptiometry (DXA) revolutionized the bone densitometry field, and improved standard care of patients with osteoporosis, when introduced more than 30 years ago [1, 2]. The most recent Position Development Conference arranged by the International Society for Clinical Densitometry (ISCD) in 2019, compiled the available evidence and issued guidance for the use of DXA [5] Adherence to these recommendations reduces technical errors and invalid conclusions. Software updates might introduce systematic differences, even within the same brand and generation of hardware [16]. The impact of different hardware/software versions, different software analysis settings and different reference populations on the BMD-t-score relationship in a longitudinal setting has not been systematically investigated. The aim was to demonstrate the implications of different hardware, software updates and software analysis settings and different reference populations for the long-term follow up of patients in clinical and research environments
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