Frequent bone density tests for senior women may not be needed, according to a new study.

In order to catch osteoporosis, Medicare pays for a bone density test every two years. But the study, published Thursday in The New England Journal of Medicine, followed nearly 5,000 women ages 67 and older for more than a decade. None had osteoporosis when they enrolled in the study, and only 10% of those with substantially low bone density developed osteoporosis within a year.

That means, the investigators suggest, that the bone-loss disease develops slowly enough that women who have normal tests at age 65 can wait up to 15 years before being tested again. Women with moderate osteopenia, a risk factor for osteoporosis, should be rescreened in five years, and women with advanced osteopenia should be rescreened in a year, the authors wrote.