Many women who get screened for osteoporosis may not need it, according to a study that suggests current guidelines result in too many unnecessary tests, increasing costs and sometimes spurring unnecessary treatment.

Osteoporosis, a loss in bone density that can cause breaks and injuries, develops in fewer than 10 percent of women at age 80, if they had normal density at age 65, according to a report today in the New England Journal of Medicine.

The U.S. Preventive Services Task Force, which sets testing guidelines, recommends a bone-density test every two years. The latest study suggests a healthy result at age 65 probably means woman can wait at least 15 years before being tested again because of how slowly the disease develops.

“There’s strong belief that the more we test, the more we are helping patients,” said Margaret Gourlay, a University of North Carolina at Chapel Hill researcher and study author. “This is a good example of why that doesn’t hold up at all.”

Osteoporosis affects about 12 million Americans older than 50, including half of all post-menopausal women at some point, the U.S. task force says. The recommendation for testing every two years was made because not enough is known about how the disease develops, the group has said.

Each screening costs about $250, Gourlay said in a telephone interview. Unnecessary tests can lead to false positives and prescriptions of drugs such as Warner Chilcott’s Actonel or Eli Lilly & Co. (LLY)’s Evista, leading to more patient risk than protection, she said.

Some doctors prescribe tests every two years because Medicare, the U.S. health plan for those 65 and older, reimburses for the exams on that schedule, Gourlay said. The research team tracked patients to gather available evidence to avoid health decisions made on “marketing, advocacy, and public beliefs that have encouraged overtesting and overtreatment,” the report said.

Just as a lack of information has caused some doctors to test too often, it has led others to ignore osteoporosis altogether, Gourlay said. Patients don’t remind doctors about osteoporosis screening, which is not as common as mammograms for breast cancer or cholesterol screening, she said.

The study followed about 5,000 mostly white women over 15 years and regularly tested their bone mass starting at age 67. Gourlay said the group’s next goals include gathering data about osteoporosis treatment in men and in women younger than 65.