Bone mineral density testing: does the evidence support its selective use in well women?
Research evidence does not support either whole population or selective bone mineral density (BMD) testing of well women at or near menopause as a means to predict future fractures. On some issues, evidence is insufficient because the research has not been done. Existing research evidence, though imperfect, indicates substantial limitations of BMD testing.
The greatest concern is that BMD measurement will misdirect treatment efforts away from the majority of women who will ultimately suffer fractures by focusing attention on the minority with low bone density. In addition, BMD testing will focus attention on BMD, only one of many risk factors, the alteration of which may or may not lead to fracture reduction.
BMD measurements are poor predictors of whether individual women will suffer future fractures. In fact, most women will be misclassified if they are sorted according to BMD scores. Regardless of the threshold chosen, most women who will suffer a hip fracture (the most consequential fracture) will be classified as normal when compared with the mean (average) BMD of women of the same age.
If women more than one standard deviation (SD) below the mean are classified as being at increased risk for fractures, then 70% of the women who will eventually suffer fractures will not come from the group identified as being at risk. At the same time, only half of the 30% of women labelled as being at increased risk will have a fracture. The other half will receive unnecessary treatment. Selecting women below two SD will not solve the problem: 87% of fractures shall be missed, and 5% of those selected will not suffer fractures.
There are problems associated with classifying women according to age matched controls. Comparing a woman's BMD to the peak bone mass of healthy young women has been advocated by an industry-sponsored study group of the World Health Organization and widely publicized by the drug and device industry. According to these standards and using 1995 British Columbia population estimates, 536,000 of the 813,560 women over age 40 (66%) would be labelled as either osteoporotic' orosteopenic'. Most of these women will not suffer fractures so in this instance most women will be unnecessarily labelled as being likely to fracture. Both the problems of using age matched and peak bone mass result from the extensive overlap between women who will and who will not fracture.
Clinical management decisions should not be altered by BMD test results, except in instances where BMD test results may help in the diagnosis of women with symptomatic conditions. In particular, BMD testing should not be used to assist in decisions regarding preventive strategies such as hormone therapy (HT), nor should it be used to establish a risk assessment of well women. In both of the latter instances, BMD test results will mislabel women more often than not.
The role of BMD testing in the care of women has not been established using research evidence. In particular, research has not linked BMD testing to changes in physicians' prescribing patterns. Therefore, only estimates are possible. Estimates of the effectiveness of BMD testing in reducing the absolute numbers of hip fractures depend on assumptions regarding rates of attendance for testing, HT use, and HT effectiveness. These are at best modest. Even with optimistic assumptions the percentage of fractures prevented would be: 0.34-3.9% (Effective Health Care Bulletin 1992); 1-6% (U. S. Congressional Office of Health Technology Assessment 1995); 0.9-6.7% (International Network of Agencies for Health Technology Assessment 1996).
The effect of knowledge of BMD test results on women's behaviour has not been established. According to at least one study, women who are advised they havelow' bone mineral density may inappropriately restrict their activity levels (including essential activities like shopping); a strategy they saw as a way to avoid risking injury to theirfragile bones'. They also worried more and became more fearful of falling. Women falsely reassured may not take appropriate steps to enhance their bone health. Women with false positive test results bear the expense and side effects of medical treatment without benefit.
The groups at greatest risk of life threatening and debilitating hip fractures are women of advanced age with multiple risk factors, regardless of BMD. Strategies which measure and treat low BMD alone, while ignoring other prominent risk factors, will likely divert limited health care funds from more effective and efficient approaches. One study found that women with five or more risk factors had a hip fracture incidence of 51.4 per 1,000 woman-years as compared to 16.3 per 1,000 in women with four or fewer risk factors. By contrast, women with BMD test results in the lowest third had almost exactly the same incidence of hip fractures as women with higher bone mineral density - 33.9 versus 33.8 per 1,000 woman years.
BMD testing and reporting increased from approximately 2,000 tests in 1989/90 to 18,679 in 1995/96. It is not coincidental that during this time period the pharmaceutical and device industries strongly supported extensive advertising to raise awareness about osteoporosis and urge both doctors and consumers to intervene. Strong public policy efforts supported by objective analyses, therefore, are needed to support clinicians and health care institutions resisting adoption of widespread BMD testing of well women.
- Bone Density
- Costs and Cost Analysis