We conducted a study of rates of transition to osteoporosis in order to help clinicians decide on BMD testing intervals for older women with normal BMD or osteopenia at the initial assessment. Our results suggest that the baseline T score is the most important determinant of a BMD testing interval. During the 15-year study period, less than 1% of women with T scores indicating normal BMD and 5% of women with T scores indicating mild osteopenia at their first assessment made the transition to osteoporosis, with an estimated testing interval of about 15 years for 10% of women in each of these groups to make the transition. This finding suggests that if BMD testing is deferred for 15 years among women with T scores greater than −1.50, there is a low likelihood of a transition to osteoporosis during that period. We found that 10% of women with moderate osteopenia and 10% of women with advanced osteopenia made the transition to osteoporosis in 5 years and 1 year, respectively. Although clinical risk factors had a minimal effect on the time estimates as a whole, a significant trend for age supported shorter testing intervals as women age. The estimated time for only 2% of women to make the transition to hip or clinical vertebral fracture before the development of osteoporosis was 5 years for women with moderate or advanced osteopenia and at least 15 years for women with mild osteopenia or normal BMD. Thus, with the use of the stated criteria for the study, consideration of the time to a hip or clinical vertebral fracture would not substantially alter recommendations for osteoporosis screening intervals based on the time to osteoporosis alone.
Recent controversy over the harms of excessive screening for other chronic diseases22–24
reinforces the importance of developing a rational screening program for osteoporosis that is based on the best available evidence rather than on health care marketing, advocacy, and public beliefs that have encouraged overtesting and over-treatment in the United States.25
Our findings provide evidence-based estimates for an osteoporosis screening interval before new hip or clinical vertebral fractures and before initiation of treatment for osteoporosis. Our results are consistent with those of Hillier et al.,8
suggesting that frequent BMD testing is unlikely to improve fracture prediction, and with those of Frost et al.,9
suggesting that age and T score are key factors in determining a reasonable interval for BMD testing. Our study extends their findings by estimating the transition time to osteoporosis before a hip or clinical vertebral fracture, with the goal of treating osteoporosis to reduce the risk of such fractures, which account for the majority of fracture-related complications among older adults.
Several features of our analysis will assist clinicians in making decisions regarding osteoporosis screening intervals. Clinicians might feel impelled to shorten the BMD screening interval for patients with osteopenia who have clinical risk factors for fracture. Our estimates for BMD testing intervals proved to be robust after adjustment for major clinical risk factors. 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. As expected, the estimated time to osteoporosis decreased with increasing age, so that an interval of 3 years, instead of 5 years, might be considered for women 85 years of age or older who have moderate osteopenia. Although the trends for BMI and estrogen use were also significant, they were less clinically relevant. If 10 years were to be considered the maximum testing interval for any woman, the BMI would not alter the recommendations for the testing intervals for each T-score range (based on a comparison of the time estimates in vs. those in ). Current estrogen use, as compared with use of estrogen in the past or no history of estrogen use, was significantly associated with higher BMD and a longer testing interval. These results were consistent with the finding of BMD loss after discontinuation of hormone therapy in the Postmenopausal Estrogen/Progestin Interventions (PEPI) trial (ClinicalTrials.gov number, NCT00000466)26
and a SOF analysis suggesting that previous hormone therapy does not provide protection against hip fracture.27
Because of the transient effect of estrogen on BMD, we do not recommend modifying the screening interval on the basis of estrogen use.
Our study had several limitations. First, our testing interval was based only on BMD transitions, with adjustment for risk factors for fracture; the potential benefits and risks of screening and its cost-effectiveness were not considered. Second, owing to limitations imposed by the data set, precise time estimates were not possible for the following analyses: 5% threshold for women with advanced osteopenia at baseline, 20% threshold for women with normal BMD or mild osteopenia at baseline (Table A in the Supplementary Appendix
), and outcome for BMD at the femoral neck among women with normal BMD at baseline (Table C in the Supplementary Appendix
). Third, 49% of the original SOF participants (4747 of 9704 women) were excluded from our analysis. About half the excluded women were not eligible for screening because they had osteoporosis at baseline, had a history of a hip or clinical vertebral fracture, or had received treatment for osteoporosis at baseline; the remaining women had too few DXA examinations to be followed longitudinally. However, the mean age and mean baseline T scores in our analytic cohort were similar to those for all SOF participants who had any DXA scans of the hip. Fourth, our analysis was limited to women 67 years of age or older; different results might have been obtained from analyses that included younger postmenopausal women or men. Finally, white women accounted for more than 99% of our sample. However, because the prevalence of osteoporosis of the hip among white women is equal to or slightly higher than the prevalence among nonwhite women by estimates from the National Health and Nutrition Examination Survey,28
the testing intervals we calculated are likely to be reasonable estimates for women of all races.
The strengths of our analysis include the large size of the cohort and the long follow-up period. Repeated BMD testing during the long follow-up period allowed precise estimation of testing intervals from event times (i.e., time to the development of osteoporosis) that were unknown, up to a time interval, for every woman in the study sample.
In conclusion, our results suggest that osteoporosis would develop in less than 10% of older, postmenopausal women during screening intervals that are set at approximately 15 years for women with normal bone density or mild osteopenia (T score, greater than −1.50) at the initial assessment, 5 years for women with moderate osteopenia (T score, −1.50 to −1.99), and 1 year for women with advanced osteopenia (T score, −2.00 to −2.49).