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Not enough people at risk of osteoporosis are getting DXA scans as recommended, because of changes in Medicare reimbursement. Meanwhile, it's being marketed to fitness enthusiasts as a way to assess body composition, even before it has been well validated for that purpose.
Facing reduced reimbursement for bone-density scanning, some manufacturers and healthcare providers have begun to offer dual-energy X-ray absorptiometry (DXA) directly to the public as the "gold standard" in measuring body composition. Promotional materials use words like "superior" and "unsurpassed" to describe DXA's accuracy in assessing body fat and muscle mass.
"A person undertaking subsequent exams can see exactly where fat is being lost (or gained) and muscle gained (or lost)," says a press release from the Washington Institute of Sports Medicine in Kirkland WA, to which "anyone can self refer themselves for this test."
In the 6 weeks since the facility began offering DXA directly to patients, it has been doing about 20 per week, says its executive director, physiologist David Parker, PhD. A referral is not legally required, he told Musculoskeletal Network, and although the center will provide any customer with a written report it does not contact the primary care physician directly.
The center uses DXA to estimate a person's ideal weight based on body composition, and to assess changes in fat and muscle at 6-8 week intervals. "It gives information you can't get anywhere else," Parker added. "It's absolutely amazing."
General Electric has also been offering free DXA body-composition testing at golf tournaments this year with its Lunar iDXA system. The Pullman Family Medicine Clinic in Pullman ID offers DXA body fat analysis as "convenient, safe, and the best precision available".
But does DXA give valid information about body composition on an individual basis? DXA technology has improved dramatically over the past decade, observes Matthew Delmonico, assistant professor of kinesiology at the University of Rhode Island, who used it to study changes in thigh muscle mass after training among older adults. But without knowing about the individual device, he said, it would be difficult to judge whether a DXA scan is sensitive enough to pick up small individual changes in muscle mass.
Delmonico is more concerned about the radiation risk. Even though the dosage of a single DXA scan is low, he points out, radiation exposures are cumulative. (Parker describes the risk as minimal, similar to several days of outside yard work or a several hours of high-altitude air travel. People who order up DXA scans at the Kirkland institute have to sign a waiver.)
DXA is used widely in clinical research to assess muscle mass or fat composition among groups of people with various clinical conditions. According to a comparative review of DXA body-composition scanning, published last month in the journal Obesity, it "may be a useful clinical tool" as an alternative to BMI for assessing body composition among the anorexic or very obese, but the "ambiguity" about its accuracy "warrants concern and holds important clinical implications." The accuracy of DXA for measurements of body composition has not been validated with tests on human cadavers, observe the authors, and the precision of newer devices has yet to be established.
Meanwhile, as to the purpose for which DXA is indisputably the gold standard, bone density testing, it is disturbingly under-utilized. An analysis of US claims data for DXA bone-density scans over the past decade shows scan rates among women 65 and older rising steadily through 2008 and then leveling off, after changes in Medicare reimbursement led to a 40% reduction in fees to clinics and physician practices for DXA. The study's authors apparently felt that the implications for fracture rates among the increasing number of elderly Americans were too obvious to point out explicitly.
The Washington Institute of Sports Medicine does accept referrals for DXA bone scans, Parker said. But "bone density is not profitable for us. We can make more money on it with body composition and private pay. You see the money right up front."
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