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A second bone mineral density (BMD) test 3 years after the initial measurement did not improve the ability to assess risk of osteoporosis-related fractures in healthy postmenopausal women, according to an observational study.

Furthermore, in more than 7,000 women followed for a mean of 12 years, the initial test was more predictive of fracture risk than the second test, regardless of race, ethnicity, or age, researchers led by Carolyn Crandall, MD, of the University of California Los Angeles, reported online in .

In discriminating between women who experienced major osteoporotic fractures and those who didn't, the area under the receiver operating characteristic curve (AU-ROC) value for the baseline total hip BMD measurement was 0.61 (95% CI 0.59-0.63). For the change in total hip BMD at 3 years, the value was 0.53 (95% CI 0.51-0.55). The AU-ROC value for the combination of the two measurements was 0.61 (95% CI 0.59-0.63), Crandall's group found. Results were similar for femoral neck and lumbar spine BMD measurements.

Additionally, the study found only modest associations between 3-year change in BMD and fracture risk. For example, every one standard deviation decrease in BMD at the femoral neck at 3 years was associated with a 18% increase in major fracture risk (HR 1.18, 95% CI 1.09-1.28). In contrast, each standard deviation decrease in baseline BMD at the femoral neck was linked with a 51% risk increase (HR 1.51, 95% CI 1.37-1.67).

"Our results have clinical implications given the need to inform the optimal frequency of BMD testing. Clinicians should be aware that although change in BMD a mean of 3 years after baseline is significantly associated with fracture risk, the magnitude of this risk is modest, and change in BMD does not add meaningfully to distinguish women who experience subsequent fracture from women who do not," Crandall and colleagues wrote.

"The present results suggest that routinely repeating measurement of BMD 3 years after baseline does not have high clinical utility, especially in context of the competing demands and time constraints of the busy clinical practice setting," they noted. "Moreover, there are public health consequences of the cost and resources required to perform BMD scans that may not provide meaningfully important information for clinical decision-making regarding fracture prediction."

The study cohort included 7,419 postmenopausal women from the Women's Health Initiative. Their mean age at baseline was 66 and 77% were white. The study was unique, the researchers said, in that it included a larger proportion of younger postmenopausal women: 44% were younger than 65. Participants were followed for a mean of 12.1 years from 1993 through 2010. During follow-up, 139 women (1.9%) experienced hip fractures, and 732 women (9.9%) experienced a major osteoporotic fracture.

Asked for his opinion of the study, Michael McClung, MD, founding director of the Oregon Osteoporosis Center in Portland and member of the Board of Trustees for the North American Menopause Society (NAMS), said in an email, "This is a useful study, confirming in a large and well-studied population what we already knew -- that BMD values change very slowly in healthy postmenopausal women who are several years beyond the menopausal transition. As a result, short-term monitoring of BMD values has little clinical utility in such women. However, this conclusion requires some important qualifications and perspective."

Those qualifications include that the women in the study were healthy and at low fracture risk. The average BMD values were in the normal range, and most participants would not meet guideline criteria for baseline BMD testing, said McClung, who was not involved in the study. Additionally, women with a previous history of osteoporotic fracture, the strongest risk factor for subsequent fractures, were not included, he noted.

"The conclusion that follow-up BMD testing of healthy postmenopausal women is not clinically valuable does not pertain to women with osteoporosis or at high fracture risk, who have medical problems that predispose to bone loss, or who are taking osteoporosis medications," McClung explained.

Additional limitations of the study, the authors noted, included its observational design. Although the researchers controlled for many confounders including age, race/ethnicity, history of fracture, physical activity, body mass index, physical function, and falls in the last year, they could not rule out the possibility of residual confounding, they said. In addition, fractures were self-reported on annual questionnaires.

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