Longitudinal changes in bone mass after one year as measured by different techniques in patients with osteoporosis.

Bone mass was measured in 49 postmenopausal women by the following techniques: single photon absorptiometry at the radius (SPA), dual photon absorptiometry at the lumbar spine (DPA), quantitative computed tomography at the lumbar spine with an area of interest of only trabecular bone (QCT) or of an integrated cross-section of the vertebral body (QCTi), and total body calcium by neutron activation analysis (TBCa). Each women had two measurements with a one-year interval. Half of them were treated with calcium supplementation only; the other half also received calcitriol (1,25 dihydroxycholecalciferol). The aim of this report was to compare the changes of bone mass as measured by the different techniques. The DPA and QCTi values were significantly lower at one year than at baseline (by paired t-tests). The mean percent changes (+/- SD) for the measurements were: TBC, -0.4 +/- 4.6%; SPA-1, 1.2 +/- 7.1%; SPA-2, 0.7 +/- 6.0%; DPA, -2.5 +/- 11%; QCT, 6.5 +/- 23%; and QCTi, -6.0 +/- 9%. The percent changes by one technique did not show significant correlation to the percent changes by the other methods. We conclude that the precision of the methods in this clinical setting is not sufficient to show correlations after only one year; in addition, there may have been different rates of changes at different sites of the skeleton.