Repeat BMD: how thin is the evidence?
A 70-year-old woman presents for follow-up of hypertension. Her medical history includes hypercholesterolemia and a remote history of cigarette smoking. She has been doing well and is up to date on her breast and colon cancer screening. Her chart reveals that she had a bone mineral density (BMD) test at age 65, with T scores of -1.5 (left total hip), -1.8 (right total hip), and -1.9 (total lumbar spine). She has continued to exercise and take the calcium and vitamin D supplements that she's been taking since menopause. You consider repeating the BMD test but wonder if additional testing will add value in assessing her future fracture risk. You are considering "at risk" to be a T score of less than -2.5 (osteoporosis).
Does a repeat BMD test add additional information for assessing fracture risk, compared with the initial study?
You go to PubMed (www.pubmed.gov) and, using the MeSH browser, construct a search using the terms "bone density" AND "risk assessment."
According to the Web site of the Centers for Medicare and Medicaid Services, patients whose physicians say that they are at risk for osteoporosis can have a BMD test conducted every 2 years or more often if medically necessary (coinsurance and deductibles apply). The troubling clinical question has been: How frequently should patients be tested? The evidence from this study sheds some light on this. The evidence is reliable given the size of the cohort and the 95% follow-up completion rate. Limitations of this study are appropriately cited by the authors, namely, that women who get a repeat BMD test may be a healthier cohort. Therefore, this article speaks to the operating characteristics of initial and repeat BMD tests in healthy older women. Importantly, this study does not answer the question about the utility of the test when current therapeutic interventions, such as bisphosphonates, are given.
You discuss with the patient that she should continue to exercise and take her 1,200 mg of calcium and 400 IU of vitamin D a day. You decide against another BMD test, at least for this year. She requests that you schedule a general medical exam, and you tell her that the utility of an annual exam will be explored in a future Mindful Practice column.
T.A. Hillier et al.
Assessing the value of repeat bone mineral density measurement and prediction of fractures in older women: The study of osteoporotic fractures. Arch. Intern. Med. 2007;167:155-60.
* Design and Subjects: The prospective cohort in the current study were a subset of patients enrolled in the Study of Osteoporotic Fractures. That study was funded through the National Institutes of Health and recruited 9,704 community-dwelling women, 65 years of age or older, in Baltimore County, Md.; Minneapolis; and the Monongahela Valley near Pittsburgh.
* Measurements: Between 1989 and 1990, 8,141 women in the Study of Osteoporotic Fractures had a BMD test. All of these women were invited to participate in another study with a test a mean of 8 years later beginning in 1997. A total of 4,124 had a repeat test.
* Outcomes: Participants were contacted every 4 months by postcard or telephone to obtain information about incident hip and nonspine fractures. Incident nonspine fractures were physician adjudicated from radiology reports.
Spine fractures were diagnosed by morphometric analysis of lateral and thoracic and lumbar spine x-ray films.
* Analyses: The utility of a BMD test to discriminate between fracture and no fracture was assessed in four ways: initial BMD test alone; repeat test alone a mean of 8 years later; change in BMD between the two examinations; and a combined model of initial BMD plus the change in BMD between the two examinations. Models were adjusted for age and weight change and stratified according to estrogen levels.
The authors excluded incident nonspine and hip fractures. Also, 8% of women taking alendronate at the repeat test were excluded to eliminate confounding.
* Results: The 4,124 women with repeat tests had a mean age of 72 years and a mean initial T score of -1.37 (total hip) and mean repeat total hip BMD of -1.64. Participants experienced an average BMD loss of -0.59% per year (range 4.1% gain per year to 6.6% loss per year).
During a mean of 5 years of follow-up after the repeat BMD test, this cohort of women had 877 incident nontraumatic nonspine fractures, including 275 incident hip fractures. During a mean of 11.4 years between lateral x-ray examinations, 340 morphometric spine fractures were identified. The initial and the repeat BMD measurements were highly correlated (r = 0.92, P less than .0001).
After adjusting for age and weight change, the initial and repeat BMD measurements were similarly associated with risk for nonspine, spine, and hip fractures. None of the models (initial BMD, repeat BMD, or initial BMD plus change in BMD) were significantly different in their ability to discriminate nonspine, spine, or hip fractures. Stratification by initial BMD T scores, high bone loss, or hormone therapy did not alter the results.
BY JON O. EBBERT, M.D., AND ERIC G. TANGALOS, M.D.
DR. EBBERT and DR. TANGALOS are with the Mayo Clinic in Rochester, Minn. They have no conflicts of interest to report. To respond to this column or suggest topics for consideration, write to Dr. Ebbert and Dr. Tangalos at our editorial offices or e-mail them at email@example.com.
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|Title Annotation:||MINDFUL PRACTICE; bone mineral density|
|Author:||Ebbert, Jon O.; Tangalos, Eric G.|
|Publication:||Internal Medicine News|
|Article Type:||Case study|
|Date:||Apr 15, 2007|
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