How often do older women need bone scans? What study says

(CBS/AP) Many aging women worry about osteoporosis. But does that mean they should have frequent bone density tests? A new study suggests frequent screenings aren't necessary.

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If an initial bone scan shows no big problems, most women can safely wait 15 years to have another one, the study suggests.

Government advisers and leading doctor groups urge osteoporosis screening, but no one has known for sure how often that should happen. The findings offer the best information to date on that question, experts said.

"This is landmark, in the sense that it could allow us to move on to more precise guidelines," said Dr. Heidi Nelson, a researcher at the Oregon Health & Science University who is an expert on the topic.

The scans in question are bone mineral density tests, which usually are done through X-rays and cost around $250. The test takes about 10 minutes and involves less radiation than what's emitted during a chest X-ray. Medicare pays for testing every two years.

The test measures how thick bones are in certain spots, usually focusing on the hip and lower spine. Doctors use it to get an early warning of osteoporosis, a bone-thinning disease that can be staved off with better diet and exercise and treated with bone-building drugs. Nearly half of all women older than 50 will break a bone because of osteoporosis, according to the National Osteoporosis Foundation.

the U.S. Preventive Services Task Force, a government panel that issues testing guidelines, recommends that all women over 65 get a scan. The panel also recommends testing for younger postmenopausal women who seem at higher risk for fractures. But the task force has not said how often follow-up tests should be done, just that a couple years between tests are needed.

The research - published in the Jan. 19 New England Journal of Medicine - involves nearly 5,000 women aged 67 years and older in a national health study that began in the 1980s. None had osteoporosis at the outset. The researchers looked at how the women did on bone density tests, and followed them for 15 years to see who got osteoporosis and when. And they found that women with a healthy initial test could wait as long as 15 years before getting a second screening. But women deemed at moderate risk should get tested about every five years. And women at high risk should get tested more often, perhaps even annually.

The results feed some concerns that tests are done too often.

"It's an expenditure of time, it's exposure to radiation, and it's cost. And there's no reason to expose yourself to any risks if there's going to be no benefit," explained Dr. Virginia Moyer, who heads the the task force.

Study author Dr. Margaret Gourlay of the University of North Carolina worries that her findings might be misinterpreted and cause some women to wait longer than they should for their next test. She cited earlier research suggesting not enough women get the recommended initial scan.

The 15-year interval applies only to postmenopausal women judged to be at low risk for osteoporosis from the first screening, she noted, and perhaps fewer than half of U.S. women over 65 fall into that category. And even for those women, Gourlay said, other risk factors have to be considered: smoking, slim build, prior broken bones and taking medication that has an eroding effect on bones.

She also noted that osteoporosis becomes a greater risk in the oldest patients, so a woman with a moderate risk who is 85 or older might be better off getting tested every three years instead of every five.

WebMD has more on osteoporosis.