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More than one million Americans undergo bone density scans each year, looking for evidence of osteoporosis that would increase their risk for fracture. But there's been no clear evidence that osteoporosis screening helps to reduce fracture risk.

"Although some groups recommend screening, no study had proven that screening prevents fractures. Our study provides new evidence for the effectiveness of osteoporosis screening," said lead researcher Dr. Lisa Kern, Assistant Professor of Public Health and Medicine at Weill Medical College of Cornell University in New York City. Dr. Kern is also Assistant Attending Epidemiologist at NewYork-Presbyterian Hospital/Weill Cornell Medical Center.

Dr. Kern and her colleagues found that screening for osteoporosis with bone density scans was associated with 36% fewer hip fractures over six years compared with usual medical care. The study will be published in the February 1 issue of the Annals of Internal Medicine.

Despite the fact that bone density screening has become routine for many post-menopausal women, debate continues among experts as to the utility of this procedure in preventing fracture. While both the National Osteoporosis Foundation and the U.S. Preventive Services Task Force recommend screening for all women 65 years of age and older, a consensus development panel at the National Institutes of Health did not endorse screening, citing a lack of evidence to support its use.

Dr. Kern's study included 3107 women and men over the age of 65 who were participants in the Cardiovascular Health Study. Participants already diagnosed with osteoporosis or a previous hip fracture and those taking bisphosphonate drugs were excluded. The study took place in California, Pennsylvania, Maryland, and North Carolina. In 1994-1995, only the participants from California and Pennsylvania had scans to measure bone density. The researchers sent the results of the scans to participants and their primary care doctors. Prescription of any osteoporosis treatment was left up to the participants and their doctors. The researchers followed participants for up to 6 years and collected information about hip fractures by using hospital records.

Hip fractures occurred in 33 screened people (about 5 fractures per 1000 person-years) and 69 usual-care people (about 8 fractures per 1000 person-years).

"This difference was statistically significant, but there were some otherdifferences between the groups besides screening that could partially explain the difference in hip fractures," Dr. Kern said. "Surprisingly, differences in the prescription of vitamin D, calcium, estrogen, and bisphosphonates didnot seem to account for all of the difference in hip fractures."

The study did not collect information on behavior changes such as increased physical activity or use of fall-prevention strategies, which might help account for the benefit in those who were screened.

Although the study was not a randomized trial, it used the best available methods to evaluate the effectiveness of screening. "It would be difficult to randomize people to screening because bone density scans are widely used now," Dr. Kern explained. "The results of our study may be of interest to clinicians and to groups that are drafting guidelines on osteoporosis screening."

Funding for the study was provided by the National Heart, Lung, and Blood Institute; the Robert Wood Johnson Foundation; the National Institute on Aging; and the National Institute of Diabetes and Digestive and Kidney Diseases.

Co-authors include Dr. Neil R. Powe and Dr. Linda P. Fried of Johns Hopkins University, Baltimore, MD; Dr. Michael A. Levine of The Cleveland Clinic Foundation, Cleveland, OH; Dr. Annette L. Fitzpatrick of the University of Washington, Seattle, WA; Dr. Tamara B. Harris of the National Institute on Aging, Bethesda, MD; and Dr. John Robbins of the University of California at Davis, CA.