BODY-COMPOSITION BY DXA - TRIED AND TRUE

Dual-energy x-ray absorptiometry (DXA) is unquestionably the method of choice for the assessment of bone mass. Recent generations of DXA ins truments also have the capability of assessing soft tissue mass, there by providing a three-compartment model of body composition, i.e., bone mineral, fat, and bone-free lean masses. Although hydrodensitometry h as long been considered the reference method of assessing body composi tion, assumptions regarding the constancy of the constituents of fat-f ree mass may compromise its validity in some populations. Because DXA appears to be less dependent on assumptions regarding biological consi stency, it is possible that it has the potential to provide a more acc urate assessment of body composition across populations than does hydr odensitometry, and that it should be considered the reference method. DXA has been shown to provide precise measures of body composition, bu t it remains questionable as to whether those measures are accurate. C ontributing to the uncertainty regarding validity is the variability a mong manufacturers of DXA instruments in the methods of calibration, d ata acquisition, and data analysis. Although DXA holds great promise i n becoming the criterion method of assessing body composition, and has been promoted as such by some investigators, available data indicate that this endorsement is premature.