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Biomechanical CT cost-effective alternative to DXA for osteoporosis screening
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Among older adults who undergo an abdominal CT scan, an osteoporosis screening that uses biomechanical CT data may serve as a cost-effective alternative to usual care, particularly as DXA screening rates remain low, according to findings from a modeling analysis published in the Journal of Bone and Mineral Research.
According to U.S. Medicare data, only 9.5% of women and 1.7% of men aged at least 65 years undergo a recommended bone mineral density test via DXA scan, and the sensitivity of traditional DXA for predicting fracture is modest, Maria Pisu, PhD, associate professor of medicine at the University of Alabama at Birmingham, and colleagues wrote in the study background. As an alternative, finite element analysis of clinical-resolution CT scans could provide noninvasive estimates of the breaking strength of the hip and spine, the researchers wrote. Combining that measurement with a CT-based measurement of a DXA-equivalent BMD T-score could provide a more comprehensive assessment of osteoporosis vs. using bone strength or BMD alone, they noted.
“Thus, in any managed care system, it is highly feasible for ancillary [biomechanical] CT to be offered in a standing-order fashion to all screen-eligible patients undergoing abdominal or hip-containing CT when an osteoporosis screen is medically indicated,” Pisu and colleagues wrote. “With many millions of abdominal CT scans taken annually, such standing-order [biomechanical] CT-based screening in managed care systems could be clinically impactful if exploited for patients already undergoing CT — while continuing to rely on usual-care screening for all other patients.”
Pisu and colleagues analyzed data from a hypothetical cohort of 1,000 women and men aged at least 65 years who received an abdominal CT (in year 1) for any medical reason who did not undergo a recent DXA scan and were not taking an osteoporosis medication.
In analyses stratified by sex, the researchers compared two screening strategies: participation in the biomechanical CT program or usual care. Under the biomechanical CT strategy, all patients undergo a biomechanical CT test at year 1, with patients testing positive classified as high risk and eligible for 2 years of alendronate therapy. Researchers assumed for analyses that 50% of patients prescribed treatment filled prescriptions and were 100% adherent to therapy over 2 years.
Under the usual care strategy, the 1,000 patients were assumed to be screened by DXA each year at typical annual screening rates observed for Medicare patients aged at least 65 years — 9.5% for women and 1.7% for men. Other parameters were similar to the biomechanical CT strategy. For simplicity of modeling, researchers focused only on hip fractures. Researchers also assessed no screening and no treatment to calculate the absolute number of prevented hip fractures.
The researchers found that biomechanical CT provided a greater clinical benefit at a lower cost vs. usual care. In the base model, biomechanical CT prevented 3.1 hip fractures per 1,000 women over 5 years and 1.9 hip fractures per 1,000 men over 5 years, and increased quality-adjusted life-years (2.95 per 1,000 women; 1.48 per 1,000 men), whereas usual care prevented 2.4 hip fractures per 1,000 women and 0.2 per 1,000 men over 5 years.
“Efficacy and savings increased further for higher-risk patient pools, greater treatment adherence and longer treatment duration,” the researchers wrote.
In analysis adjusting the sensitivity and specificity of biomechanical CT to parallel DXA measurements, the number of prevented hip fractures fell to 2.7 per 1,000 women and 1.5 per 1,000 men over 5 years.
The researchers noted that the findings are theoretical, although the results for clinical efficacy are consistent with available real-world clinical data.
“One large driver of overall cost-effectiveness is the cost of treating hip and other fractures that would otherwise occur without the screening and treatment program,” the researchers wrote. “Our effective total care cost of $50,000 during the first year after hip fracture is supported by numerous studies and may even be conservative.”
The researchers concluded that biomechanical CT screening results should go to the health care professional who ordered the test and who is charged with interpreting the results, and followed up with patient care.
“Since millions of patients age 65 and older already undergo abdominal CT each year in the U.S., the current results suggest that use of ancillary [biomechanical] CT may have a positive impact on the management of osteoporosis,” the researchers wrote. – by Regina Schaffer
Disclosures: Pisu reports she has received salary support paid to her institution via an NIH grant awarded to O.N. Diagnostics. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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Robert Blank, MD, PhD
This study addresses two serious problems surrounding osteoporosis care.
First, it addresses the fact that bone mineral density as measured by DXA has only moderate predictive ability for fracture despite being the best test available in clinical practice today. Each T-score unit decrease in BMD confers approximately a doubling of fracture risk. Thus, while the risk for fracture is approximately fourfold higher in an individual with a T-score of –3 than in an individual with a T-score of –1, most osteoporotic fractures occur in individuals who do not have an osteoporotic range BMD. This is so because the pool of individuals with a higher BMD is so much larger. Note also that the World Health Organization explicitly calls for a diagnosis of osteoporosis in an individual who suffers a low-trauma fracture regardless of BMD. The failure of BMD to align more closely with the observed occurrence of fractures causes a great deal of confusion among patients and providers.
Second, this study addresses the fact that screening rates for osteoporosis are low and falling. I believe that this is a multifactorial problem. The issues outlined in the preceding paragraph contribute. Other contributing factors include consolidation of medical practices with a consequent decline in the number of DXA testing facilities, lack of bandwidth among primary care practitioners to address the many medical problems older patients face, and a failure to appreciate the mechanistic link between osteoporosis and fracture.
Use of “opportunistic” CT scans, obtained to investigate problems other than fracture risk, has recently emerged as a promising approach to addressing the low screening rate. It is already established that a virtual DXA scan performed by software manipulation of quantitative CT data provides comparable diagnostic information to an actual DXA scan of the hip. It has also been established that finite element analysis of the hip, as used in this study, is able to predict hip fracture risk.
The authors and O.N. Diagnostics, the study sponsor, have here reported a modeling study that shows that their software implementation of hip finite element analysis has the potential to address the current gaps in osteoporosis screening in a cost-effective manner, with efficacy comparable or superior to existing screening protocols. Regardless of whether or not the details of their analysis are correct in every detail, robustness of the findings across sensitivity analyses show that the overall message is on-target. Armed with these data, O.N. Diagnostics is currently petitioning the FDA for approval of the software. Readers may be justifiably cautious in interpreting the findings given the evident, fully acknowledged interest of these authors in the validity of their method.
In my opinion, it is desirable that we find better ways to predict fractures and that we screen widely for low-trauma fracture risk. We have an array of drugs with proven fracture prevention efficacy. These can be complemented by a variety of additional measures to optimize diet, home safety and mobility. Given the high burden of fracture-associated mortality, morbidity and expense, coupled with the aging of our population, we have the potential to prevent a great deal of suffering by identifying those who will benefit from interventions to prevent fractures. This work shows one way in which this might be accomplished.
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