#32 Bone Mineral Density – Too much of a good thing?
CLINICAL QUESTION
Once we have initiated bisphosphonate therapy, how frequently should we check bone mineral density (BMD)?
BOTTOM LINE
Repeating BMD in the first three years after starting treatment with a bisphosphonate is unnecessary and potentially confusing.1 The vast majority of patients taking a bisphosphonate will get an adequate increase in BMD after three years and have a reduced fracture risk regardless of BMD changes.
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EVIDENCE
Secondary analysis of the Fracture Intervention Trial:
- 6,459 patients randomized to alendronate or placebo with annual BMD testing for three years.1
- Mean increase in hip BMD of 0.030 g/cm2 in the alendronate group. compared to a mean decrease of 0.012 g/cm2 with placebo.
- Individuals’ BMD readings were more variable than readings between people.
- Alendronate increased BMD 0.013 g/cm2 per year but individuals’ readings varied by a similar amount (0.012 g/cm2, standard deviation).
- Alendronate resulted in “sufficient” (≥0.019 g/cm2) increases in hip BMD for 97.5% of patients after three years.
- Fracture Intervention Trial also demonstrated that women who took alendronate with decreased BMD2 still had a reduction in fracture risk.
- Dual-energy x-ray absorptiometry BMD measurement precision has important limitations.
- 535 patients scanned twice over 2-4 weeks demonstrated variability at the hip of 2.4% (trochanter) to 5% (Ward’s triangle).3
- Precision of measurements decline with decreasing BMD.4
- Canadian 2010 clinical practice guidelines recommend repeating BMD 1-3 years after initiating therapy5
- However, average rate of bone loss in postmenopausal women is 0.5-2% per year while most treatments increased BMD of 1-6% over three years.6
- Given these very small changes, only a very precise test will detect short-term changes.
- BMD readings are too imprecise to reliably discern annual small changes on therapy.
- Most follow-up BMD measurements while on bisphosphonate do not result in treatment changes, even when there is a significant decrease in BMD.7
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