Many women who get screened for the bone-thinning disease osteoporosis may not actually need such testing, a new study suggests.

A number of expert guidelines say that women age 65 or older should get a bone scan to screen for osteoporosis, a condition in which bones become fragile and vulnerable to breaks. Some women with risk factors for osteoporosis, such as smoking, are advised to start screening around age 50.

But in the new study, researchers found that of 615 women who underwent osteoporosis screening at Connecticut clinics, 41 percent did not meet those criteria.

Exactly why they were tested is not clear from the study, according to lead researcher Dr. Peter F. Schnatz, of the Reading Hospital and Medical Center in Pennsylvania.

In some cases, women might ask for screening, he told Reuters Health. Or some doctors may not be aware of the guidelines and believe, for example, that it's best to screen all postmenopausal women.

Whatever the reasons, "the findings are certainly not encouraging," Schnatz said.

That's because like most screening, testing for osteoporosis has downsides.

Screening is usually done with a special type of x-ray that measures bone density, known as dual-energy X-ray absorptiometry (DXA). While the bone scan is simple and non-invasive, it is not cheap—typically ringing up at $200 to $300.

More importantly, Schnatz said, unwarranted DXA screening may lead to some women being treated unnecessarily.

After the test, a woman is given a "T-score," which is a comparison of her bone mass against the average bone mass of a healthy, young woman. In some cases, a woman may have relatively low bone mass, though not overt osteoporosis, and the doctor may feel "compelled to treat," Schnatz said.

Treatment may include bisphosphonate medications like Fosamax, hormones or the drug Evista,which mimics the beneficial effects of estrogen on bone.

Those therapies can carry side effects—including serious, though uncommon, risks like increased odds of stroke, breast cancer, and heart disease in women taking estrogen, and blood clots in those using Evista, according to past research. Bisphosphonates have been linked to rare cases of thigh bone fractures and bone death of the jaw.

The current findings, reported in the journal Menopause, are based on 615 women who underwent DXA screening in the Hartford, Connecticut, area.

Schnatz and his colleagues determined how many of those women met screening guidelines issued in 2006 by the North American Menopause Society (NAMS).

Those guidelines recommend DXA screening for all women age 65 and up. Women ages 50 to 64 may be candidates if they have certain risk factors for osteoporosis—including smoking, a history of a "fragility" fracture since going through menopause, low body weight (under 127 pounds) and having a parent who suffered a hip fracture.

In 2010, NAMS added daily alcohol consumption and rheumatoid arthritis to its list of risk factors that should prompt earlier screening.

The guidelines are in line with those from other medical groups, like the American College of Obstetricians and Gynecologists.

They are also similar to recommendations issued earlier this year by the U.S. Preventive Services Task Force (USPSTF), an expert panel supported by the federal government.

The panel said that for women ages 50 to 64, doctors should consider risk factors like smoking, drinking and low body weight, and then estimate a woman's risk of having a bone fracture in the next 10 years. If she has the same risk as the average 65-year-old woman would—a roughly nine percent chance over 10 years—then screening would make sense.

According to Schnatz, the bottom line for women is to be aware of the screening guidelines, and if a doctor does recommend DXA testing, don't be afraid to ask questions.

"Make sure you understand why screening is being recommended," he said.

But while the current findings suggest that some women have osteoporosis screening when they don't need it, they also point to a problem of under-treatment.

That is, among women who were screened and met NAMS guidelines for osteoporosis treatment, 35 percent were not on any type of therapy. And more than half—53 percent—were not getting regular exercise, which is recommended for protecting bone mass.

Again, Schnatz said, the reasons for the finding are unclear. The researchers don't know, for example, how often women were offered treatment, but declined.

It would be helpful, Schnatz said, for future studies to try to weed out the reasons why some women are screened when they don't meet guidelines, and why others are not treated even though they do.

Larger studies of more diverse groups of women would also be useful, he said. A limitation of the current study is that all of the women were from a single U.S. city, so it's not clear whether the results would be the same nationwide.

It's estimated that about 12 million Americans older than 50 have osteoporosis, and roughly half of postmenopausal women will suffer an osteoporosis-related fracture at some point.

Indeed, another recent study found a rise in fracture risk in older women after they go off hormone replacement therapy. (See Reuters Health story of August 29, 2011).

To help prevent bone loss with age, experts recommend getting a well-balanced diet with enough calcium and vitamin D, in particular, as well as regular exercise.