Comparison of radiographic absorptiometry with dual-energy X-ray absorptiometry and quantitative computed tomography in normal older white and black women

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Abstract
Bone mineral density (BMD) of the phalanges of the hand was measured by the technique of radiographic absorptiometry (RA) in 199 older postmenopausal women previously determined to have normal BMD by dual‐energy x‐ray absorptiometry (DXA) and quantitative computed tomography (QCT). The average age of the women was 66.8 ± 4.9 years, and they were 19.9 ± 6.7 years postmenopause. In the 54 black women, phalangeal BMD was 11.7% greater than in the 145 white women, a difference comparable to that found using DXA at the radial midshaft, the lumbar spine, and femoral neck. A correlation matrix comparing BMD measured by RA to BMD measured by DXA and QCT indicates that, in general, RA was related to the various DXA and QCT measurement sites as well as these sites were related to each other. When results for RA, DXA, and QCT obtained in our cohort of older women were compared to available reference data for peak adult bone mass, the average difference (SD units) from peak value was greatest for RA (‐1.77 radius, −1.24 spine, −2.13 femoral neck, −2.34 QCT spine, and −2.71 phalanges). We conclude that RA is an acceptable measure of phalangeal BMD and that the data in our cohort can serve as reference data for older white and black women aged 55–75 years. Once the ability of RA to predict future fracture occurrence has been demonstrated, it could be rapidly deployed as a low‐cost, widely available bone mass measurement technique.