Comparison of single-photon and dual-energy x-ray absorptiometry of the radius.

We compared dual-energy x-ray absorptiometry (DXA) for measurement of the radius with the conventional single-photon absorptiometry (SPA) method. To evaluate reproducibility, 34 healthy male and female subjects were measured twice each by both methods. While the instruments measured bone mineral content (BMC) similarly, projected area was consistently lower by SPA and therefore bone mineral density (BMD) was higher by an average of 10%. We report similar coefficients of variation for the two methods, which are 0.8% (SPA) and 0.7% (DXA) for BMC (P = 0.71) and 0.8% (SPA) and 1.4% (DXA) for BMD (P = 0.02). We also evaluated the relationship between the methods with data from 196 clinic patients who were measured once each on both instruments. The BMD measurements from the two instruments were highly correlated (r = 0.97) in these patients, which permits the conversion of databases from SPA to DXA-equivalents. We conclude that DXA can replace SPA for radial bone densitometry.