Vol 56: december • décembre 2010 Canadian Family Physician•Le Médecin de famille canadien
1299
Tools for Practice
Bone mineral density testing
Too much of a good thing?
Christina Korownyk
MD CCFPG. Michael Allan
MD CCFPMichael R. Kolber
MD CCFPClinical question
Once we have initiated bisphosphonate therapy, how often should we check bone mineral density (BMD)?
Evidence
Secondary analysis of the Fracture Intervention Trial:
• 6459 patients randomized to receive alendronate or placebo, with annual BMD testing for 3 years.1
-Mean increase in hip BMD of 0.030 g/cm2 in the alendronate group compared with 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 (SD 0.012 g/cm2).
-Alendronate resulted in “sufficient” (≥ 0.019 g/cm2) increases in hip BMD for 97.5% of patients after 3 years.
• The Fracture Intervention Trial also demonstrated that women with decreased BMD2 who took alendronate still had reductions in fracture risk.
Context
• Dual-energy x-ray absorptiometry BMD measurement precision has important limitations.
-535 patients scanned twice over 2 to 4 weeks dem- onstrated variability in BMD at the hip of 2.4% (tro- chanter) to 5% (Ward’s triangle).3
-Precision of measurements declines with decreasing BMD.4
• Canadian 2010 clinical practice guidelines recommend repeating BMD 1 to 3 years after initiating therapy.5 -However, average rate of bone loss in postmeno-
pausal women is 0.5% to 2.0% per year, while most treatments increased BMD 1% to 6% over 3 years.6 -Given these very small changes, only a very precise
test will detect short-term changes.
• Measurement of BMD is too imprecise to reliably dis- cern the small annual changes resulting from therapy.
Bottom line
Repeating BMD testing within 3 years of starting treatment with bisphosphonates is unnecessary and potentially confusing.1 By far most patients taking bisphosphonates will have adequate increases in BMD after 3 years and will have a reduced fracture risk regardless of BMD changes.
Implementation
Osteoporosis is the risk factor and surrogate marker for the clinically meaningful end point of symptomatic frac- ture. To estimate baseline fracture risk, Canadian guide- lines5 recommend tools like CAROC,7 based on age, sex, and T score for the femoral neck, or FRAX, a complex online tool.8 Evidence suggests that more complex pre- diction models such as FRAX do not significantly improve fracture prediction over simple tools based on age and BMD9 or BMD alone in early postmenopausal women.10 If your BMD reports do not include an assessment of frac- ture risk, a simple table or graph of CAROC can be found at the Osteoporosis Canada website.7 Once bisphospho- nate therapy has been initiated, repeat BMD measure- ments are not routinely necessary before 3 years’ time.
Dr Korownyk is Assistant Professor in the Department of Family Medicine at the University of Alberta in Edmonton. Dr Allan is Associate Professor in the Department of Family Medicine at the University of Alberta. Dr Kolber is Associate Professor in the Department of Family Medicine at the University of Alberta.
The opinions expressed in this Tools for Practice article are those of the authors and do not necessarily mirror the perspective and policy of the Alberta College of Family Physicians.
references
1. Bell KJ, Hayen A, Macaskill P, Irwig L, Craig JC, Ensrud K, et al. Value of routine moni- toring of bone mineral density after starting bisphosphonate treatment: secondary analysis of trial data. BMJ 2009;338:b226. DOI: 10.1136/bmj.b2266.
2. Chapurlat RD, Palermo L, Ramsay P, Cummings SR. Risk of fracture among women who lose bone density during treatment with alendronate. The Fracture Intervention Trial. Osteoporos Int 2005;16:842-8.
3. Wahner HW, Looker A, Dunn WL, Walters LC, Hauser MF, Novak C. Quality control of bone densitometry in a national health survey (NHANES III) using three mobile examination centers. J Bone Miner Res 1994;9(6):951-60.
4. Laskey MA, Flaxman ME, Barber RW, Trafford S, Hayball MP, Lyttle KD, et al.
Comparative performance in vitro and in vivo of Lunar DPX and Hologic QDR-1000 dual energy x-ray absorptiometers. Br J Radiol 1991;64:1023-9.
5. Papaioannou A, Morin S, Cheung AM, Atkinson S, Brown JP, Feldman S, et al. 2010 clin- ical practice guidelines for the diagnosis and management of osteoporosis in Canada:
summary. CMAJ 2010 Oct 12 [epub ahead of print]. DOI: 10.1503/cmaj.100771.
6. Brown JP, Josse RG; Scientific Advisory Council of the Osteoporosis Society of Canada. 2002 clinical practice guidelines for the diagnosis and management of osteoporosis in Canada. CMAJ 2002;167(10 Suppl):S1-34.
7. Osteoporosis Canada. Assessment of 10-year fracture risk—women and men. Toronto, ON: Osteoporosis Canada; 2010. Available from: http://osteoporosis.bluerush.ca/
www/pdf/caroc_oct_2010.pdf. Accessed 2010 Oct 23.
8. World Health Organization Collaborating Centre for Metabolic Bone Diseases. FRAX. WHO fracture risk assessment tool. Calculation tool. Sheffield, UK: University of Sheffield. Available from: www.shef.ac.uk/FRAX/tool.jsp?locationValue=9. Accessed 2010 Sep 27.
9. Ensrud KE, Lui LY, Taylor BC, Schousboe JT, Donaldson MG, Fink HA, et al. A com- parison of prediction models for fractures in older women: is more better? Arch Intern Med 2009;169(22):2087-94.
10. Trémollieres FA, Pouillès JM, Drewniak N, Laparra J, Ribot CA, Dargent-Molina P.
Fracture risk prediction using BMD and clinical risk factors in early postmenopausal women: sensitivity of the WHO FRAX tool. J Bone Miner Res 2010;25(5):1002-9.
Tools for Practice articles in Canadian Family Physician are adapted from articles published twice monthly on the Alberta College of Family Physicians (ACFP) web- site, summarizing medical evidence with a focus on topical issues and practice-modifying information. The ACFP summaries and the series in Canadian Family Physician are coordinated by Dr G. Michael Allan, and the summaries are co-authored by at least 1 practising family physician. Feedback is welcome and can be sent to toolsforpractice@cfpc.ca. Archived articles are available on the ACFP website: www.acfp.ca.
