ASSESSMENT OF CHANGES IN DUAL-ENERGY X-RAY ABSORPTIOMETRY PERFORMANCEFOLLOWING A SYSTEM UPGRADE

System upgrades are a constant feature of many highly technical specia lities and are normally assumed to have a negligible effect on patient data. We report on the assessment of an upgrade made to a Norland XR- 26 dual-energy X-ray absorptiometry (DXA) system. The upgraded version (2.3) consisted of new hip positioning aids, hip image analysis softw are and updates to the normal ranges. Measurements of femoral neck and trochanteric bone mineral density correlated well between versions (r = 0.969 and r = 0.971), those for femoral neck and trochanteric bone mineral content less well (r = 0.956 and r = 0.911), and Ward's triang le values and femoral neck area measurements were poorly correlated (r = 0.719-0.881). The upgrade was claimed to improve precision while re ducing analysis and imaging time. Improved precision was not demonstra ted, with good precision found both before and after the upgrade. Corr elation between femoral neck Z-scores were good for the European norma l range (r = 0.970), but unacceptable for the UK range (r = 0.769). Th ese correlations were not close enough to allow patients scanned with the old version to be followed up with scans using the upgrade. The up grade was, however, preferred for new attenders because of the improve d speed and automation of hip analysis, without loss of precision. The most important implication in terms of patient management was the cha nge made to the UK normal range, which had a very large effect on the number of patients deemed to be at risk from osteoporosis. It is essen tial that any upgrade introduced to an existing DXA system is carefull y evaluated, since it may affect system performance and patient result s.