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#32 Bone Mineral Density – Too much of a good thing?

Once we have initiated bisphosphonate therapy, how frequently should we check bone mineral density (BMD)?

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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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 
updated by ricky jan 10 2018

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  • Christina Korownyk MD CCFP
  • Michael R Kolber MD CCFP MSc

1. Bell KJ, Hayen A, Macaskill P, et al. BMJ. 2009; 338:b2266.

2. Chapurlat RD, Palermo L, Ramsay P, et al. Osteoporos Int. 2005; 16:842-8.

3. Wahner HW, Looker A, Dunn WL, et al. J Bone Miner Res. 1994 Jun; 9(6):951-60.

4. Laskey MA, Flaxman ME, Barber RW, et al. Br J Radiol. 1991; 64:1023-9.

5. Papaioannou A, Morin S, Cheung AM, et al. CMAJ. 2010; 182(17):1864-73.

6. Brown JP, Josse RG, Scientific Advisory Council of the Osteoporosis Society of Canada. CMAJ. 2002; 167(10 suppl):S1-S34.

7. Combs BP, Rappaport M, Caverley TJ, et al. JAMA Intern Med. 2013; 173:2008-9.

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.