In vitro comparability of dual energy X-ray absorptiometry (DEXA) bone densitometers.

Six Hologic QDR-1000 DEXA bone densitometers at different centers across the USA were compared to determine the intermachine variability. Nine scans in succession were acquired on each machine using a single anthropomorphic lumbar spine phantom (manufactured by Hologic). Values for BMC, area, and BMD were recorded for each measurement. Means, standard deviations (SD), and coefficients of variation (CV) were calculated for each machine. All the CVs (BMC, area, BMD) were less than 1% (range 0.3%-0.6%). The CV of the means at the six sites were 0.4%, 0.6%, and 0.5% for BMC, area, and BMD, respectively. Although several significant differences for BMC, area, and BMD were noted by ANOVA between machines at different sites, the difference between the highest and lowest means of the individual machines was only 1.1%, 1.31%, and 1.07% for BMC, area, and BMD. The small variations between the DEXA systems are encouraging for researchers involved in multicenter trials in which data are pooled.