25 November, 2013

Screening for osteoporosis with bone mineral density (BMD) is recommended for older adults; however, it is unclear whether repeating a BMD screening test improves fracture risk assessment. The aim of the study presented below was to determine whether changes in BMD after 4 years provide additional information on fracture risk beyond baseline BMD and to quantify the change in fracture risk classification by the FRAX model after a second BMD measure [1].

The cohort included 310 men and 492 women from the Framingham Osteoporosis Study with two measures of femoral neck BMD taken from 1987 through 1999. Participants were followed through 2009 or 12 years following the second BMD measure. Patients with a history of hip fracture were excluded. The mean age was 74.8 years. Less than one-quarter had normal basal BMD (T-score up to 1), a little more than one-half had osteopenia (T-score between 1 and 2.5), and almost one-quarter were osteoporotic. The mean (standard deviation, SD) BMD change was −0.6% per year (1.8%). Throughout a median follow-up of 9.6 years, 76 participants experienced an incident hip fracture and 113 participants experienced a major osteoporotic fracture. Annual percent BMD change per SD decrease was associated with risk of hip fracture (hazard ratio (HR) 1.43; 95% CI 1.16–1.78) and major osteoporotic fracture (HR 1.21; 95% CI 1.01–1.45) after adjusting for baseline BMD. At 10 years' follow-up, 1 SD decrease in annual percent BMD change compared with the mean BMD change was associated with 3.9 excess hip fractures per 100 persons. Using the net reclassification index, a second BMD measure increased the proportion of participants reclassified as at high risk of hip fracture by 3.9% (95% CI −2.2% to 9.9%), whereas it decreased the proportion classified as at low risk by −2.2% (95% CI −4.5% to 0.1%).

The conclusion was that, in untreated men and women of mean age 75 years, a second BMD measure after 4 years did not meaningfully improve the prediction of hip or major osteoporotic fracture. Repeating a BMD measure within 4 years to improve fracture risk stratification may not be necessary in adults of this age untreated for osteoporosis.

Comment

Several previous studies focused on the issue whether BMD change improves fracture prediction beyond baseline BMD. This has both medical and economic perspectives, since any conclusions dictate the frequency of repeat BMD testing, and the corresponding budget that should be allocated by national health services or health maintenance organizations. As an example, the US Preventive Services Task Force recommends waiting a minimum of 2 years to obtain a second BMD measure but notes that 'longer intervals may be necessary to improve fracture prediction' [2].

Another major issue, often investigated, is whether any fracture risk calculation score, such as FRAX, can provide reliable fracture prediction even without BMD results. It is quite clear that the combination of BMD and clinical risk factors (CRFs) predicts fractures better than BMD or CRFs alone [3].

The Framingham project is actually a life-long, very tight follow-up program, which observes and records vast amounts of data related to a well-defined white population living in one area in the United States. This is its value, but also its limitation, since results may not be generalized to other communities or countries with different ethnic populations. The median hip fracture risk score (interquartile range) using the second BMD test was 4.6%, and the mean annual change in hip BMD was −0.6%. For major osteoporotic fractures, every SD decrease in annual percent BMD change was associated with an HR of 1.21 for risk of fracture after adjusting for baseline BMD. The investigators concluded that repeating a BMD test after 4 years would rarely change the clinical management of osteoporosis based on risk scores of hip fracture. Individuals with the greatest changes in risk scores were those who would have already been classified as at high risk based on historic BMD and updated clinical characteristics. However, for major osteoporotic fractures, a second BMD measure appeared somewhat more useful.

Whether these recommendations will be regarded as useful remains to be seen, but my guess is that they will not change the current practice for determining the frequency of BMD testing. The short 'Limitation' section at the end of the article exposes many material problems: BMD measurements were done by two different machines/scanners and, therefore, inter-machine and intra-machine precision errors could result in misclassification of risk. Only the surviving participants of the Framingham project were available, of course, for the second BMD testing, and thus from a lifetime perspective of a prevention program, there was a selection bias. Patients with a history of hip fracture and patients receiving estrogen were excluded. There was no data on use of medications (except estrogen). There were no data on parental or family history of hip fracture. Last, but not least, the specific cohort was old and the retrieved data are certainly not applicable to people in their fifties or sixties, the people we want to target as well in our fracture prevention programs.

Amos Pines
Department of Medicine 'T', Ichilov Hospital, Tel-Aviv, Israel

References

1. Berry SD, Samelson EJ, Pencina MJ, et al. Repeat bone mineral density screening and prediction of hip and major osteoporotic fracture. JAMA 2013;310:1256-62. http://www.ncbi.nlm.nih.gov/pubmed/24065012

2. US Preventive Services Task Force. Screening for osteoporosis. Ann Intern Med 2011;154:356-64. http://www.ncbi.nlm.nih.gov/pubmed/21242341

3. Lewiecki EM. Bone density measurement and assessment of fracture risk. Clin Obstet Gynecol 2013 Sep 6. Epub ahead of print. http://www.ncbi.nlm.nih.gov/pubmed/24022502