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Intervention thresholds for osteoporosis |
Kanis J A, Johnell O, Oden A, De Laet C, Oglesby A, Jonsson B |
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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 health interventions examined in the study were several treatments for the prevention of hip fracture in women at different levels of risk for osteoporosis. The interventions, such as vitamin D with calcium, bisphosphonate or hormone replacement therapies, were not explicitly compared, but a range of efficacy levels, which the authors stated reflected the efficacy of these treatments, was considered.
Study population The study population comprised the general female population at several levels of risk for osteoporotic fractures.
Setting The setting was the community. The economic study was carried out in Sweden.
Dates to which data relate Data on effectiveness were derived from studies published between 1980 and 2000. No dates for resource use were reported. No price year was indicated.
Source of effectiveness data The effectiveness data were derived from previously published studies supported by the authors' assumptions.
Modelling A Markov model was constructed to model the cost-effectiveness of the interventions at different relative risk (RR) values of hip fracture and at any given age in the general population of women in Sweden over a period of five years, plus a waning of effect for five years. Details on the decision model (such as the health states) were not explicitly reported.
Outcomes assessed in the review The health outcomes assessed from the published studies were age-specific utilities derived from the EuroQol (EQ5D) for hip fractures and for other fractures; the RR reduction of hip fractures due to the intervention; hip fracture and other osteoporotic fracture rates; utility losses related with hip fractures; excess morbidity and excess mortality.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included Fourteen primary studies were used as the source of the effectiveness data.
Methods of combining primary studies Narrative methods were used.
Investigation of differences between primary studies Results of the review Age-specific utilities derived from the EuroQol (EQ5D) for hip fractures and for other fractures were not reported.
The RR reduction of hip fractures due to the intervention was 35% in the base case.
Utility losses were 0.2 quality-adjusted life-years (QALYs) in the first year and 0.1 in the second and subsequent years.
Excess morbidity was 3.34 in women between the ages of 50 and 55 and decreased with age to approximately 1.25 between the ages of 85 and 89.
Excess mortality was not reported.
Methods used to derive estimates of effectiveness The authors made some assumptions to support the data used in the decision model.
Estimates of effectiveness and key assumptions The authors assumed that, after stopping the intervention, the risk reduction reversed in a linear manner over a five year period; that age-specific rates for osteoporotic fractures did not change over individuals' lifetimes; that excess mortality after fracture was included for the first year after fracture and was the same as that of the general population for the second and subsequent years. Hip fracture and other osteoporotic fracture rates were not reported.
Measure of benefits used in the economic analysis The benefit measure used in the economic analysis was the QALY. A 3% discount rate was used as the time horizon of the study was five years.
Direct costs A 3% discount rate was used as costs were incurred over a period of 5 years. Unit costs and quantities of resources were not reported separately. The economic evaluation included the costs of intervention (diagnosis, drugs, and monitoring) and the cost-savings due to the reduced number of hip fractures due to the efficacy of the intervention. Fracture costs were estimated as the difference between costs during the years after fracture and costs in the year preceding the fracture. Costs of the intervention also included the costs of selecting women for treatment. The cost/resource boundary adopted appears to have been that of the health care system. The cost of the intervention in the base case was $500. The estimation of costs was based on published Swedish data. The source of the quantities of resources used was not reported. Total costs were calculated using modelling. No price year was given.
Statistical analysis of costs Costs were treated deterministically in the base case.
Indirect Costs Indirect costs were not included.
Currency Costs were estimated in Swedish kroner (Sek), but were converted into US dollars ($) at an exchange rate of $1=Sek10.
Sensitivity analysis Sensitivity analyses (presumably univariate) were carried out to assess the robustness of the estimated cost-utility ratios to variations in several parameters used in the decision model. In particular, different intervention cost levels were tested ($200, $300, and $400 per annum) and different efficacy levels (10%, 20%, and 50%), reflecting the effectiveness of several treatments available. And finally, different 10-year probability values for hip fracture were considered.
Estimated benefits used in the economic analysis The total number of QALYs was not reported.
Cost results Total costs were not reported.
Synthesis of costs and benefits An average cost-utility analysis was performed. No incremental analysis was conducted. The critical threshold value of the cost-utility analysis was a value of $60,000 per QALY gained. The main result of the analysis was that the cost-effectiveness improved with age, due to a higher fracture risk and a decrease in intervention costs due to higher mortality, and with higher RR. In the base case (35% effectiveness and a cost of $500 per annum), it was cost-effective to treat women at average risk at the age of 70 years and even more cost-effective in older women; the RR threshold at which treatment became cost-effective was 1.02 at the age of 65 years, 1.49 at 60 years, and 2.38 at 55 years. At the age of 50 treatment was cost-effective only at a very high risk (RR=3.9). Similar results were obtained when a threshold of $30,000 per QALY gained was used (when the costs of added years were excluded). In the sensitivity analyses, the RR at which interventions became cost-effective decreased with lower costs and increased with lower effectiveness. The threshold of 10-year probability value at which the intervention was cost-effective ranged from 1.4% at the age of 50 to 4.1% at the age of 65 years. The study results did not change when a threshold of $50,000 per QALY gained was used.
Authors' conclusions The authors concluded that different subgroups of women (with different age and risk rates) may be treated cost-effectively. Major determinants of cost-effectiveness were the age of the individual, the cost of the intervention and the relative risk of fractures (not only hip fractures).
CRD COMMENTARY - Selection of comparators The authors did not explicitly consider specific treatments to prevent osteoporotic fractures, but only specific efficacy rates. Thus any treatment may, in theory, be considered as the comparator if its efficacy is similar to the values reported in the present study.
Validity of estimate of measure of effectiveness The effectiveness estimates were based on data derived from several published studies. However, no formal review of the literature was undertaken and the impact of differences between the primary studies was not taken into account in the analysis. In addition, the authors acknowledged that several assumptions were used in the decision model and their impacts on the overall conclusions of the analysis were not easy to quantify. As a consequence, the effectiveness results should be interpreted with caution.
Validity of estimate of measure of benefit QALYs were used as benefit measure in the economic analysis and appear to have been appropriate. The use of QALYs permits the comparison of the cost-effectiveness of the intervention under study with other procedures implemented in the health care system. However, the method by which the QALYs were derived was not explicitly reported and few details of the decision model were provided.
Validity of estimate of costs The analysis of costs appears to have been carried out from the perspective of the Swedish health system. Indirect costs were not included. Cost estimates were based on actual data derived from published sources and were specific to the Swedish setting. Several sensitivity analyses were conducted to analyse different scenarios. However, unit costs were not reported separately from quantities of resources used and no price year was given. Finally, an incremental analysis was not performed, thus calling into question claims regarding whether any of the technologies (represented by a level of efficacy) would be cost-effective. A necessary condition to determine whether an intervention is cost-effective is to compare it to the next best alternative, which in this case would be the next level of efficacy.
Other issues The authors compared their findings with those from other studies. The issue of the generalisability of the study results was not explicitly addressed and the authors stated that the model and the data used in the analysis were specific to Sweden. Thus the external validity of the study was quite low, also due to the fact that unit costs were not reported. The model referred to the general female population in Sweden and this was reflected in the conclusions of the study. The authors also noted that the use of assumptions in the analysis may have represented a limitation of the study.
Implications of the study The main implication of the study was that targeted treatments for the prevention of osteoporotic fractures in the general population of women at different risk levels may be cost-effective. However, this conclusion was sensitive to several factors, such as the age of the patient and the cost and efficacy of the treatment and guidelines due to the lack of incremental analysis as discussed above.
Source of funding The authors are grateful to Lilly Research Centre, Hologic, Novartis, and Roche for their support of these studies.
Bibliographic details Kanis J A, Johnell O, Oden A, De Laet C, Oglesby A, Jonsson B. Intervention thresholds for osteoporosis. Bone 2002; 31(1): 26-31 Indexing Status Subject indexing assigned by NLM MeSH Aged; Aged, 80 and over; Cost-Benefit Analysis /economics /statistics & Female; Hip Fractures /economics /prevention & Humans; Middle Aged; Models, Biological; Osteoporosis /economics /prevention & Risk Factors; control; control; numerical data AccessionNumber 22002001339 Date bibliographic record published 31/03/2003 Date abstract record published 31/03/2003 |
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