Single X-ray absorptiometry: performance characteristics and comparison with single photon absorptiometry.

The aim of the present study was to evaluate a new device for measurement of forearm bone mass using the technique of single X-ray absorptiometry (SXA, DTX-100; Osteometer A/S, Rødovre, Denmark), and to compare the performance with the more traditional single photon absorptiometry (SPA, DT 100; Osteometer A/S, Rødovre, Denmark). The SPA phantom measurements showed a coefficient of variation of 0.43% and 0.42% for bone mineral content (BMC) and bone mineral density (BMD), respectively (39 months including seven source changes). The SXA precision errors were slightly lower with values of 0.30% and 0.30%, respectively. The patient measurements showed SPA coefficients of variation of 0.85% and 0.99% (BMC and BMD) and SXA coefficients of variation of 0.56% and 0.83%, respectively. The correlation between SPA and SXA values performed in 377 individuals yielded r values of 0.99 and 0.98 for BMC and BMD, respectively. The correlations between SXA measurements of the dominant and non-dominant forearm yielded an r-value of 0.95, with a slope of 0.949 (p < 0.001) and an intercept of 0.204 (p < 0.05). The non-dominant forearm thus had approximately 3% lower BMC than the dominant (the same was true for BMD). Correlations to spine and femur ranged from r = 0.48 to r = 0.75. In conclusion, the new single X-ray absorptiometry forearm bone densitometer described in this paper has performance characteristics which allows it to be used both for diagnostic purposes and for the follow-up of treatment.