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Economic comparison of diagnostic approaches for evaluating osteoporosis in older women |
Kraemer D F, Nelson H D, Bauer D C, Helfand M |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The study examined three diagnostic strategies for the assessment of osteoporosis in older women. The strategies were:
dual-energy X-ray absorptiometry of the hip or femoral neck (DXA-FN) alone;
calcaneal quantitative ultrasound (QUS) alone; and
a sequential approach with QUS first and then DXA-FN for those with low QUS scores.
A T-score of less than or equal to -2.5 was used to define osteoporosis based on the DXA-FN. Different QUS cut points (from 50 to 85 decibels/megahertz, dB/MHz) were used in the analysis (lower values represent higher fracture risk).
Economic study type Cost-effectiveness analysis.
Study population The study population comprised a hypothetical cohort of older women (70 years and older).
Setting The setting was primary and secondary care. The economic study was carried out in the USA.
Dates to which data relate The effectiveness data and some resource use data were derived from studies published in 1997 and 1998. The costs were estimated using 1999 and 2000 prices.
Source of effectiveness data The effectiveness data was derived from a synthesis of published studies.
Modelling A decision model was constructed to predict the clinical and economic outcomes of the three diagnostic procedures in a hypothetical cohort of 1,000 older women. The model estimated the number of women identified for treatment, the number of hip fractures prevented, the number of women needed-to-treat (NTT) to prevent one hip fracture, and the total costs of the three strategies. The model was restricted to hip fractures during a 2-year follow-up period. Therefore, sequelae of hip fractures (i.e. death or admission to a nursing home) were not taken into consideration. All women diagnosed as osteoporotic received bisphosphonate treatment. The structure of the decision tree was represented graphically.
Outcomes assessed in the review The outcomes estimated from the literature were:
data on BMD using DXA-FN,
QUS values,
the incidence of hip fractures,
fracture risk reduction with bisphosphonate treatment, and
the mortality rate.
Study designs and other criteria for inclusion in the review Much of the data on the diagnostic approaches were obtained from the Study of Osteoporotic Fractures (SOF) cohort. This included a final sample of 5,993 women with both DXA-FN and QUS measurements. The fracture risk reduction with bisphosphonate treatment (alendronate) was obtained from the National Osteoporotic Foundation, while average mortality came from US life tables. It appears that a systematic review of the literature has not been undertaken.
Sources searched to identify primary studies Criteria used to ensure the validity of primary studies The authors did not comment on the validity of the primary studies.
Methods used to judge relevance and validity, and for extracting data Number of primary studies included Three primary studies provided the clinical data.
Methods of combining primary studies The primary studies were not combined.
Investigation of differences between primary studies Results of the review The overall hip fracture rate in the SOF cohort was 0.9% over a 2-year follow-up period.
Using DXA-FN alone, approximately 28% of women were identified as osteoporotic (T-score -2.5 or less) and had a higher fracture rate (2.08%) than those with a T-score above -2.5 (0.44%).
The hip fracture rates were also higher for women identified as high-risk using QUS at all cut points.
The fracture risk reduction with bisphosphonate treatment was 50%.
The multiplier of overall fracture risk was 100%.
The reduction in efficacy (fracture rate reduction) following diagnosis with QUS alone was 0%.
The mortality rate was based on the average mortality rate for females in the USA with the same age as the cohort mean (76 years).
Measure of benefits used in the economic analysis The benefit measures used were the number of hip fractures prevented and the NNT to prevent one fracture. These measures were estimated using the decision model but were not combined with the costs. Therefore, in effect, a cost-consequences analysis was carried out.
Direct costs The analysis of the costs appears to have been carried out from the perspective of the third-party payer. Three main categories of costs were included: diagnosis costs, hip fracture costs and treatment costs. The unit costs were not presented separately from the quantities of resources used for all items, and a detailed breakdown of the cost items was not provided. Only the unit costs of DXA-FN and QUS were reported. Diagnosis costs were estimated using Medicare reimbursement rates for 2000, hip fracture costs were obtained from the US Congress Office of Technology Assessment, and treatment costs were derived from the National Osteoporosis Foundation. An annual discount rate of 3% was applied as the long-term costs were evaluated. Diagnosis costs were estimated in 2000, while hip fracture and treatment costs were updated to 1999 values using medical inflation data from the US Bureau of Labor.
Statistical analysis of costs The costs were treated deterministically.
Indirect Costs The indirect costs were not included in the economic evaluation.
Sensitivity analysis Univariate sensitivity analyses were carried out to assess the robustness of the base-case results to variations in clinical (fracture risk and treatment effect) and economic inputs. The ranges of values were derived from the literature or were arbitrarily set by the authors.
Estimated benefits used in the economic analysis The number of hip fractures prevented per 1,000 women was 2.92 with DXA-FN alone. The number ranged from 1.50 to 2.92 with the sequential strategy and from 1.84 to 4.51 with QUS alone, depending on the QUS cut point (the higher the cut point, the greater the number of hip fractures prevented).
In particular, the QUS strategy led to higher benefits (more fractures prevented) for cut points higher than 65 dB/MHz in comparison with DXA-FN alone. The sequential strategy was associated with lower benefits in comparison with DXA-FN alone for QUS cut points lower than 80 dB/MHz, and equal benefits for a cut point of 80 or 85 dB/MHz.
The NNT to prevent one fracture was 96 with DXA-FN alone. It ranged from 63 to 91 with the sequential strategy and from 89 to 193 with QUS alone, depending on the QUS cut point (the higher the cut point, the greater the NNT).
The estimated benefits were quite robust to variations in the clinical inputs. The variables with the greatest impact were hip fracture rate, hip fracture risk reduction and treatment efficacy. However, the basic patterns remained unchanged.
Cost results The total costs per woman were $532 with DXA-FN alone. Such costs ranged from $177 to $523 with the sequential strategy and from $262 to $1,365 with QUS alone, depending on the QUS cut point (the higher the cut point, the higher the cost).
In particular, the QUS strategy led to higher costs for cut points higher than 60 dB/MHz in comparison with DXA-FN alone. The sequential strategy was associated with lower costs in comparison with DXA-FN alone for all cut points.
The cost results were robust to variations in most model inputs.
Synthesis of costs and benefits A synthesis of the costs and benefits was not relevant as a cost-consequences analysis was carried out.
Authors' conclusions For older women referred for testing, a sequential diagnostic approach based on calcaneal quantitative ultrasound (QUS) followed by dual X-ray absorptiometry of the hip and femoral neck (DXA-FN) for those with low values of QUS could prevent similar numbers of hip fracture to a strategy based on DXA-FN alone, while reducing the total number of women treated and hence the total costs. The analysis revealed that a clear definition of cut points for QUS is a key issue. In fact, the comparison between QUS and DXA-FN alone led to different results using different cut points. For a cut point lower than 65 dB/MHz, the QUS strategy was less effective and less costly, while for cut points higher than 65 dB/MHz, the QUS strategy was more effective but more costly.
CRD COMMENTARY - Selection of comparators The authors justified the choice of the comparators, which were appropriate for the study question. DXA-FN can be considered as the 'gold' standard for the diagnosis of osteoporosis, while QUS is a less expensive diagnostic technique available in the USA. You should decide whether these are valid comparators in your own setting.
Validity of estimate of measure of effectiveness The effectiveness evidence was obtained from published sources, which were identified selectively. Hence, a systematic review of the literature was not undertaken. Most of the clinical data came from the SOF cohort, but the validity of the primary sources was not discussed. Thus, it was difficult to assess the robustness of the primary estimates. Other data came from the National Osteoporosis Foundation. The issue of comparability of the primary data was not addressed. The authors performed sensitivity analyses to assess the impact of changes in primary estimates on the results of the analysis.
Validity of estimate of measure of benefit No summary benefit measure was used in the analysis because a cost-consequences analysis was conducted. Please refer to the comments in the 'Validity of estimate of measure of effectiveness' field (above). Summary model outputs were not combined with the costs.
Validity of estimate of costs The analysis of the costs was consistent with the perspective adopted. Limited information on the unit costs and quantities of resources used was provided, which limits the possibility of replicating the analysis in other settings. The sources of the costs were reported, whereas those for resource consumption were not explicitly stated. Statistical analyses were not carried out to test the statistical significance of differences in the costs. The cost estimates were specific to the study setting but were varied in the sensitivity analysis. The years of the prices used to derive cost estimates were reported and the authors took inflation rates into account.
Other issues The authors applied their analysis to a cohort of French women achieving results similar to those observed in the current analysis. The issue of the generalisability of the study results to other settings was not explicitly addressed and some sensitivity analyses on the costs were performed. The authors noted the limitations of their analysis. For example, the need of a more complex model, the need to consider a broader age range, the use of a cost-utility framework, a societal perspective, and a longer timeframe. They also pointed out that optimistic assumptions about treatment effects were made, which might have affected the validity of the analysis.
Implications of the study The study results suggest that a sequential approach based on QUS, to determine which women should be tested with DXA-FN, led to lower total costs and reduced the NNT in comparison with a DXA-FN alone approach. The authors stated that a clinical trial or a well-designed observational study should be performed to corroborate the results of the current study.
Source of funding Funded by grants from the Public Health Service.
Bibliographic details Kraemer D F, Nelson H D, Bauer D C, Helfand M. Economic comparison of diagnostic approaches for evaluating osteoporosis in older women. Osteoporosis International 2006; 17(1): 68-76 Other publications of related interest Bauer DC, Gluer CC, Cauley JA, et al. Broadband ultrasound attenuation predicts fractures strongly and independently of densitometry in older women. A prospective study. Arch Intern Med 1997;157:629-34.
US Preventive Service Task Force. Screening for osteoporosis in postmenopausal women: recommendations and rationale. Ann Intern Med 2002;137:526-8.
National Osteoporosis Foundation. Osteoporosis: review of the evidence for prevention, diagnosis, and treatment and cost-effectiveness analysis. Executive Summary. Osteoporos Int 1998; Suppl:S3-S6.
Indexing Status Subject indexing assigned by NLM MeSH Absorptiometry, Photon /economics; Aged; Bone Density; Calcaneus /physiopathology /ultrasonography; Cost-Benefit Analysis; Decision Support Techniques; Female; Femur Neck /physiopathology; Health Care Costs /statistics & Hip Fractures /economics /etiology /prevention & Humans; Middle Aged; Oregon; Osteoporosis, Postmenopausal /complications /diagnosis /economics /therapy; control; numerical data AccessionNumber 22006000181 Date bibliographic record published 30/09/2006 Date abstract record published 30/09/2006 |
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