INSTRUMENT PERFORMANCE IN BONE-DENSITY TESTING AT 5 AUSTRALIAN CENTERS

Aims: To assess the in vitro precision and accuracy of bone mineral de nsitometry (BMD) within and between locations at five Australian centr es. Methods: Using a multicentre reliability study the accuracy and sh ort-and long-term precision of dual-energy X-ray absorptiometry (DXA) in vitro was compared on five instruments. Measures were performed usi ng pencil beam mode on four Hologic QDR-2000 densitometers and one Hol ogic QDR-1000/W (Hologic Inc, Waltham, MA). Results: Short-term precis ion of bone mineral density measurement was less than 0.5% for spine p hantoms (n=10 for each centre, mean intrasite coefficient of variation [CV] 0.39+/-0.09% [SD]) and for hip phantoms (n=10 for each centre, m ean intrasite coefficient of variation [CV] 0.34+/-0.10% [SD]). Betwee n-centre measurement (n=10 for each phantom) of a single spine phantom and a single hip phantom (specified mineral contents - 58.5 g and 38. 6 g, respectively) revealed ranges of bone mineral content of 57.7-58. 1 g (all-point CV=0.52%) and 37.1-37.8 g (all-point CV=0.70%), respect ively. When results from pairs of machines were compared there were st atistically different mean BMD results for the majority of the ten pos sible pairings for both spine and hip measurements. Each study centre measured in vitro stability of phantom BMD measurements over a one yea r period (n=45-283 median 157 for spine; and n=0-262, median 38, for h ip); CVs ranged from 0.38 to 0.53% for the spine measurements and from 0.38 to 0.54% for the hip measurements. The mean all-point accuracy o f the spine phantom measurements was 99.1% and the hip phantom measure ments was 96.7%. Conclusions: Across a number of instruments DXA demon strates in vitro all-point precision of 0.5% for the spine phantom and 0.7% for the hip phantom. The instrument demonstrates accuracy of gre ater than 99% at the spine and 96% at the hip. This finding has clinic al, research and quality control implications.