The study, published in Thursday’s issue of The New England Journal of Medicine, is part of a broad rethinking of how to diagnose and treat the potentially debilitating bone disease that can lead to broken hips and collapsing spines.
A class of drugs, bisphosphonates, which includes Fosamax, have been found to prevent fractures in people with osteoporosis. But medical experts no longer recommend the medicines to prevent osteoporosis itself. They no longer want women to take them indefinitely, and no longer consider bone density measurements the sole defining factor in deciding if a woman needs to be treated.
Now, with the new study, researchers are asking whether frequent bone density measurements even make sense for the majority of older women whose bone density is not near a danger zone on initial tests, recommended at age 65.
In an interview, Gourlay said that the study can be used as the basis of discussions between women and their doctors about how often osteoporosis screening should be performed after an initial test.
"These results are strong enough that we should be screening women who have good bone density on their first test less often than the women who have lower levels of bone density," she said, pointing to the dramatic difference between the women with normal bone mineral density or mild osteopenia and those with more brittle bones.
Bone mineral density testing with dual-energy x-ray absorptiometry (DXA) to screen for osteoporosis is recommended for all women 65 and older, although there are few data to determine the optimal interval between tests.
Gourlay and colleagues set out to address that uncertainty using data from the Study of Osteoporotic Fractures (SOF). The current analysis included 4,957 women 67 and older who had either normal bone mineral density (T score at the femoral neck and total hip of -1.00 or higher) or osteopenia (T score of -2.49 to -1.01).
The women did not have a history of hip or clinical vertebral fracture and had not been treated for osteoporosis. The researchers followed them for up to 15 years.
The testing interval for the subgroups of women was defined as the time needed for 10% to make the transition to osteoporosis before having a hip or clinical vertebral fracture or receiving osteoporosis treatment.
During follow-up, the percentage of women who developed osteoporosis was 0.8% for those with normal bone mineral density and 4.6%, 20.9%, and 62.3% for those with mild, moderate, and advanced osteopenia.
The estimated testing intervals for the four groups of declining bone mineral density were 16.8, 17.3, 4.7, and 1.1 years, which remained robust after adjustment for major clinical risk factors for fracture.
"However, clinicians may choose to reevaluate patients before our estimated screening intervals if there is evidence of decreased activity or mobility, weight loss, or other risk factors not considered in our analyses," the researchers wrote.
Gourlay said that age and body mass index are the most important factors to consider in addition to bone density.
There was a significant trend that supported shorter testing intervals as women age. For example, the estimated time to transition from moderate osteopenia to osteoporosis was about five years for women age 70 and three years for those age 85.
In addition, if a patient is very thin, it is more likely she will have lower bone density, Gourlay said.
Although Gourlay said the findings could make an impact in the clinic immediately, she and her colleagues acknowledged some limitations, including the lack of information on the potential risks and benefits and cost-effectiveness of screening.
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