Bone-density testing interval and transition to osteoporosis in older women

Abstract

Background: Although bone mineral density (BMD) testing to screen for osteoporosis (BMD T score, -2.50 or lower) is recommended for women 65 years of age or older, there are few data to guide decisions about the interval between BMD tests.

Methods: We studied 4957 women, 67 years of age or older, with normal BMD (T score at the femoral neck and total hip, -1.00 or higher) or osteopenia (T score, -1.01 to -2.49) and with no history of hip or clinical vertebral fracture or of treatment for osteoporosis, followed prospectively for up to 15 years. The BMD testing interval was defined as the estimated time for 10% of women to make the transition to osteoporosis before having a hip or clinical vertebral fracture, with adjustment for estrogen use and clinical risk factors. Transitions from normal BMD and from three subgroups of osteopenia (mild, moderate, and advanced) were analyzed with the use of parametric cumulative incidence models. Incident hip and clinical vertebral fractures and initiation of treatment with bisphosphonates, calcitonin, or raloxifene were treated as competing risks.

Results: The estimated BMD testing interval was 16.8 years (95% confidence interval [CI], 11.5 to 24.6) for women with normal BMD, 17.3 years (95% CI, 13.9 to 21.5) for women with mild osteopenia, 4.7 years (95% CI, 4.2 to 5.2) for women with moderate osteopenia, and 1.1 years (95% CI, 1.0 to 1.3) for women with advanced osteopenia.

Conclusions: Our data indicate that osteoporosis would develop in less than 10% of older, postmenopausal women during rescreening intervals of approximately 15 years for women with normal bone density or mild osteopenia, 5 years for women with moderate osteopenia, and 1 year for women with advanced osteopenia. (Funded by the National Institutes of Health.).

Figure 1. Study Populations for Analyses of BMD Transitions

Of the 8514 women who underwent dual-energy x-ray absorptiometry (DXA) for measurement of bone mineral density (BMD), 3557 were excluded from the study, including those who had osteoporosis (T score at the femoral neck or total hip, −2.50 or lower), those who had a past hip or clinical vertebral fracture or who received treatment for osteoporosis by the time of their first BMD measurement, and those who did not undergo BMD measurements at the femoral neck and total hip at two or more examinations. In the analytic cohort of 4957 women with adequate BMD measurements of the femoral neck and total hip before data censoring, two transitions were studied: normal BMD to osteoporosis (1255 women) and osteopenia to osteoporosis (4215 women). A total of 513 women made the transition from normal BMD to osteopenia and had at least one subsequent examination with BMD recorded; data from these women were included in both analyses.

Figure 2. Unadjusted Cumulative Incidence of Osteoporosis According to Baseline T-Score Range

The proportion of women who had a transition to osteoporosis is shown as a function of time. The cumulative incidence curves were estimated by means of parametric cumulative incidence models for interval-censored data. The dashed horizontal line marks the 10% threshold for the transition to osteoporosis; where this line intersects each cumulative incidence curve, a vertical dashed line to the x axis marks the estimated testing interval. The analysis of women with osteopenia at baseline is based on three T-score groups and included the 513 women who made the transition from normal BMD to osteopenia and had at least one subsequent examination with BMD recorded.