New research could mean millions of older American women can skip frequent screening tests for osteoporosis: If an initial bone density test shows no big problems, many 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 how often that should happen. The findings offer the best information to date on that question, experts said. 

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Weight-bearing and resistance exercises are key to good bone density. (Donna McWilliam/Associated Press)

"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.

At issues are bone mineral density tests, which usually are done through X-rays and cost around $250 US. It 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 new study feeds concerns that the tests are done too often, at least for some women.

"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 U.S. Preventive Services Task Force, a government panel that issues testing guidelines.

The test measures how thick bones are in certain spots, usually focusing on the hip and lower spine. Doctors use it to gain 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. government task force 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.

There are no immediate plans to update the task force's advice for osteoporosis screenings, but the new study will be an important consideration when the panel acts again, Moyer said.

Screening advice

The new, government-funded research 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 watched for who got osteoporosis and when. They were followed for 15 years.

Based on that, the researchers concluded 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 research, published in Thursday's New England Journal of Medicine, was led by Dr. Margaret Gourlay of the University of North Carolina. She 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.

But she said even for those women, other risk factors have to be considered:

  • Smoking.
  • Slim build.
  • Prior broken bones.
  • 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.

Osteoporosis guidelines in Canada recommend that women and men over age 50 should be assessed for risk factors for osteoporosis and fracture to identify those at high risk for fractures.

Risk groups

Dr. Angela Cheung of the University Health Network in Toronto helped to draft osteoporosis guidelines used in Canada. She said for more than a year, Canadian physicians have been working to reduce the number of bone density tests given to low-risk patients.

"There's underutilization, undertreating and undertesting in the high-risk group and we have been trying to really shift the focus from [the] low-risk to the high-risk group," said Cheung.

Those at high risk include smokers, heavy drinkers and people suffering from conditions that increase the risk of falling, such as dementia — people Cheung said need to be tested more often.

For low-risk patients, a healthy diet and exercise are recommended to help maintain good bone health.

With files from CBC's Melanie Nagy