Bone Density Scan (cont.)
Catherine Burt Driver, MD
Catherine Burt Driver, MD, is board certified in internal medicine and rheumatology by the American Board of Internal Medicine. Dr. Driver is a member of the American College of Rheumatology. She currently is in active practice in the field of rheumatology in Mission Viejo, Calif., where she is a partner in Mission Internal Medical Group.
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
In this Article
- Bone density scan facts
- What is osteoporosis?
- How does osteoporosis occur?
- What is bone mineral density (BMD)?
- Why is BMD measurement important?
- What is the relationship between BMD and fracture risk?
- Who should have BMD testing?
- How is BMD measured?
- What are other methods of measuring BMD?
- How often should DXA scans be repeated to monitor treatment?
- What is the cost of DXA?
- What about the accuracy of BMD testing in the doctor's office using smaller equipment?
- Find a local Rheumatologist in your town
How often should DXA scans be repeated to monitor treatment?
The frequency of monitoring osteoporosis treatment using DXA scans is highly controversial. Some doctors recommend DXA scanning at one- to two-year intervals to monitor changes in bone density during treatment. But recent scientific evidence questions the usefulness of such interval monitoring. Reasons why repeating bone density scans is extremely tricky include:
- Bone density changes so slowly that the changes may be smaller than the measurement error of the machine. In other words, repeat DXA scans cannot distinguish between a "real" increase in bone density or a mere variation in measurement from the machine itself. Typically, BMD changes 1% per year, which is less than the error of a DXA machine (usually in the range of 3%). Changes of less than 2%-4% in the vertebrae and 3%-6% at the hip from test to test can be due to the precision error of the method.
- Whereas the real purpose of prescription osteoporosis treatment is to decrease future bone fractures, there is no good correlation between increases in bone density as measured by DXA with decreases in fracture risks with treatment. There are multiple examples of this in recent clinical studies. For example, the improvement in BMD only accounted for 4% of the reduction in spine fracture risk with raloxifene (Evista), 16% of the reduction in spine fracture risk with alendronate (Fosamax), and 18% of the reduction in spine fracture risk with risedronate (Actonel, Atelvia). Thus, improvement in BMD does not indicate the amount of the antifracture benefit of osteoporosis medication. Prescription medication may decrease a person's risk of fracture even when there is no apparent increase in BMD. Physicians and nonphysicians alike are often surprised to learn this information!
- Even if the DXA scan shows continued deterioration in bone density during treatment, no research data exists demonstrating that changing a medication, combining medications, or increasing medication doses will be safe and helpful in decreasing the future risk of fractures compared to just continuing the same medication.
- Even if a person's bone density deteriorates during treatment, it is quite likely that the person would have lost even more bone density without treatment.
- Recent research has shown that women who lose bone density after the first year of menopausal hormone therapy will gain bone density in the next two years, whereas women who gain in the first year will tend to lose density in the next two years of therapy. Therefore, bone density during treatment naturally fluctuates and may not be indicative of the fracture protection of the medication.
Next: What is the cost of DXA?
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