DUAL X-RAY ABSORPTIOMETRY - CROSS-CALIBRATION AND NORMATIVE REFERENCERANGES FOR THE SPINE - RESULTS OF A EUROPEAN-COMMUNITY CONCERTED ACTION

Bone density measurements by dual X-ray absorptiometry (DXA) of the sp ine can now be made precisely, but there is no uniformity in reporting results and in presenting reference data. A European Union Concerted Action therefore devised a uniform procedure for cross-calibrating and standardizing instruments, using the European spine phantom (ESP) pro totype. This phantom differs in a number of respects from the final ve rsion of the ESP. Eighteen centers in nine countries obtained 1619 rec ords (1035 women) from Caucasian subjects, aged 20-80 years, drawn fro m normal populations. The DXA machines used were made by the Hologic, Lunar, and Norland companies. Highly statistically significant differe nces were evident between populations, both in apparent rates of bone loss with age and in the spread of values about the age-adjusted means . There were small residual differences in the results obtained with t he three machine brands which could have been due to the relatively la rge between-center population differences we observed. The alternative or additional explanation that they were attributable, in part, to th e design differences between the ESP prototype and the definitive ESP, which became available after this study was completed, was shown to b e a valid possibility. Results from postmenopausal women reported in r elation to the years that have elapsed since menopause showed reduced population variance when compared with conventional reporting in relat ion to age. After cross-calibration, the center with the highest age-a djusted normal density value averaged 23% more than the center with th e lowest. It is therefore crucially important to select appropriate re ference data in clinical and epidemiological studies. These results pr ovide a basis for designing protocols for multicenter studies using cu rrently installed densitometers.