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Rapid Responses: Rapid Responses published:
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So is AAA screening cost-effective?
- Simon G Thompson, Lois G Kim, Lu Gao (29 June 2009)
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The Danish health economic modelling study on AAA screening is flawed
- Leif P. Jensen, Jes S. Lindholt, Torben V. Schroeder (10 July 2009)
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The Danish health economic modelling study on AAA screening is not flawed
- Lars Ehlers, Kjølby M, Christensen S, Bech M, Overvad K, Sørensen J (20 August 2009)
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Simon G Thompson, Director MRC Biostatistics Unit, Institute of Public Health, Cambridge CB2 0SR, Lois G Kim, Lu Gao
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The UK is currently introducing a national screening programme for abdominal aortic aneurysm (AAA) in men aged 65. So the conclusion by Ehlers and colleagues from their health economic modelling study that screening is not cost effective appears worrying [1]. However their conclusion conflicts with that from the 10-year follow-up of the randomised Multicentre Aneurysm Screening Study (MASS) published in the same issue of the BMJ [2], our own detailed long-term modelling exercise based on the individual patient data in MASS [3,4], as well as other recent modelling studies. As Buxton’s editorial points out [5], the difference in cost effectiveness estimates is major: the long-term incremental cost per quality adjusted life year (QALY) gained is estimated as £43,000 by Ehlers and colleagues compared to £3000 based on MASS [3] – a difference that would lead to a different policy decision for the NHS. In order to try to understand the reasons for the difference, we have substituted the unit costs and parameter estimates provided by Ehlers and colleagues into our model based on MASS. Although the cost per QALY goes up somewhat from £3000 to around £6000, this does not begin to approach their estimate. So there must be other explanations, such as the structure of their model, the assumptions made, or parameters not presented – which cannot be investigated without further information from the authors. Two arguments make the cost effectiveness estimate from Ehlers and colleagues implausible. First, based on observed data in MASS (rather than hypothetical modelling), we showed directly that the cost effectiveness after 10 years was £9400 per QALY [2]. Previous modelling exercises, the MASS trial data, and Ehlers’ study all agree that cost- effectiveness will improve when considered over the longer term – since costs are generally up front while benefit accrues over time. So it is simply unbelievable that the lifetime cost-effectiveness ratio should be worse than that which we have already observed after 10 years. Secondly, Ehlers and colleagues present the modelled number of AAA-related deaths that accrue as a screening programme is launched in 10,000 men aged 65 per year (their figure 4), and claim that a net reduction is not reached until after 9 years. Re-running this analysis based on the data actually observed in MASS, shows that the benefit is seen even after 2 years. MASS recruited men aged 65-74, but any age-dependency within this range is not nearly enough to explain the differences with Ehlers’ estimates for men aged 65. The UK-based MASS trial provides most of the worldwide randomised evidence about the effects of AAA screening. The hypothetical modelling by Ehlers and colleagues does not agree with the data actually observed in the MASS trial. If one had to choose the basis on which to make decisions about policy, real data is surely preferred. Simon Thompson {1}, Lois Kim {2}, Lu Gao {1} {1} MRC Biostatistics Unit, Institute of Public Health, Cambridge CB2 0SR {2} London School of Hygiene and Tropical Medicine, London WC1E 7HT References 1. Ehlers L, Overvad K, Sorensen J, Chistensen S, Bech M, Kjolby M. Analysis of cost effectiveness of screening Danish men aged 65 for abdominal aortic aneurysm. BMJ 2009; 338: b2243 2. Thompson SG, Ashton HA, Gao L, Scott RAP. Screening men for abdominal aortic aneurysm: 10 year mortality and cost effectiveness results from the randomised Multicentre Aneurysm Screening Study. BMJ 2009; 338: b2307 3. Kim LG, Thompson SG, Briggs AH, Buxton MJ, Campbell HE. How cost- effective is screening for abdominal aortic aneurysms? Journal of Medical Screening 2007; 14: 46-52 4. Kim LG, Thompson SG, Buxton MJ, Briggs AH, Campbell HE. A Markov model for long-term cost-effectiveness modelling of screening for abdominal aortic aneurysms. MRC Biostatistics Unit Technical Report 2005/2 (available from www.mrc-bsu.cam.ac.uk). 5. Buxton MJ. Screening for abdominal aortic aneurysm [editorial]. BMJ 2009; 338: b2185 Competing interests: None declared |
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Leif P. Jensen, Consultant Vascular Surgeon, President of The Danish Society for Vascular Surgery Rigshospitalet, 2100 Ø, Copenhagen, Denmark, Jes S. Lindholt, Torben V. Schroeder
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This issue of the Journal contains two substantial contributions to the ongoing debate on screening of abdominal aortic aneurysms (AAA): the 10-year follow-up of the UK-based multicentre aneurysm screening study (MASS) and a Danish health economic modelling study(1;2). Both agree that AAA screening is effective in reducing mortality from aneurysm rupture, but the cost effectiveness estimate of 43.000 GBP per life year gained presented in the Danish study is far off any previous assessment. However, closer inspection reveals several errors in their hypothetic model, for instance; The model does not reflect reality The model is a progression model of AAA in which it can be small, medium or large. Each step has a possibility of rupture, and the small and medium sized AAA may also progress to the next step. The risk of rupture of “large” AAA is 6.5% annually based upon the observed risk of rupture in 5-6 cm AAA kept under surveillance in the UK small aneurysm trial(3). Thus the hypothetic model precludes that aneurysms exceed 6 cm, increasing the risk of rupture further. In addition, the model does not include cases having emergency repair without rupture. These cases constitutes one third of all emergency cases performed in Denmark, are encumbered with three times higher morbidity and mortality than elective cases(4), and are prevented like ruptured cases by screening. These errors are also mirrored in table 3 in which only 86 of 10.000 (0.86%) non-screened men are expected to die of AAA. In the real world, this figure is closer to 2.8%, as reported by MASS(2) and by the similar RCT in Denmark(5). The cost of stay in intensive care unit has been disregarded. The authors base costs of treating AAA on vascular DRG tariffs only, thereby disregarding the substantial costs of having patients treated in the intensive care unit (ICU). Since 2005 ICU stay beyond 48h is reimbursed separately with the following four DRG group numbers and tariffs: 2632 (£7,281), 2633 (£16,439), 2634 (£31,083), 2635 (£81,471)- depending upon the number and degree of failing organs Costs of surgery with fatal outcome is grossly underestimated Finally, a serious error appears in the use of the DRG tariffs in Table 1. Surgery with death occurring within 30 days is quoted to cost £5.038. However, this figure is used for reimbursement of patients who die within 48 hours – not 30 days. Again an error that markedly underestimates the real costs of treating patients with ruptured aneurysms. Based on data from the Danish vascular registry(4), which is also the source of data for the article, 44 % of the patients who die within 30 days survive more than 2 days, and spend an average of 13 days at ICU. Thus a qualified estimate of the costs for all patients who dies within 30 days is £38.668 per death occurring within 30 days. Reference List 1.Ehlers L, Overvad K, Sørensen J, Christensen S, Bech M, Kjolby MJ. Analysis of cost effectiveness of screening Danish men aged 65 for abdominal aortic aneurysm. BMJ 2009; ;338:b2243. 2.Thompson SG, Ashton HA, Gao L, Scott RAP. Screening men for abdominal aortic aneurysm: 10 year mortality and cost effectiveness results from the randomised Multicentre Aneurysm Screening Study. BMJ 2009; 338;b2307. 3.Brown LC, Powell JT. Risk factors for aneurysm rupture in patients kept under ultrasound surveillance. UK Small Aneurysm Trial Participants. Ann Surg 1999; 230:289-296. 4.Jensen LP. The Danish Vascular Registry. www.karbase.dk 5.Lindholt JS, Juul S, Fasting H, Henneberg EW. Screening for abdominal aortic aneurysms: single centre randomised controlled trial. BMJ 2005; 330:750-4. Competing interests: None declared |
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Lars Ehlers, Professor, University of Aalborg, Senior researcher, Centre of Public Health, Central Denmark Region Olof Palmes Alle 15, 8200 Aarhus, Kjølby M, Christensen S, Bech M, Overvad K, Sørensen J
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Our cost effectiveness analysis published in BMJ 2009; 338: b2243 shows that screening Danish men aged 65 for abdominal aortic aneurysm is not cost effective (when using a threshold value of £30000 per QALY) [1]. This result seems to contradict with earlier CEA results from the UK-based MASS trial. Most economist would probably agree that a decision economic model is preferable compared to a CEA conducted alongside a clinical trial [2]. Data from trials can have a low degree of external validity (i.e. generalizability to the real-world setting) and it is essential to undertake a modelling approach to simulate the screening program as it will be in real life. A screening program of 65 year old men is fundamentally different from a one-time screening of all elderly men. The latter will benefit from a higher prevalence and thus show a better cost effectiveness result. If a screening program of 65 year old men is implemented one should not expect the same results after 10 years as the published 10 year result from MASS. We therefore urge Thompson and colleges to re-run their CEA calculation with data on 65 year old men only and publish the result. The Danish model uses the same structure as a number of earlier cost effectiveness analyses of AAA screening [3]. We don’t agree that there are any errors in our model. The Danish cost effectiveness study was a part of a health technology assessment (HTA) initiated by the management of health care in Central Denmark Region. The Danish cardiovascular surgeons that now argue against the DRG-tariffs have earlier argued that these DRG tariffs actually can be used as estimates for surgical costs. We quote: ”we believe the used DRG tariffs are representative for AAA operations” (from Lindholt et al., Cost effectiveness Analysis of Screening for Abdominal Aortic Aneurysms Based on Five Year Results form a Randomised Hospital Based Mass Screening Trial, Eur J Vasc Endovasc Surg Vol 32, 2006; p. 14.) [4]. We have recently submitted an article: Christensen S, Ehlers L. Testing the generalizability of national reimbursement rates with respect to local setting: the costs of abdominal aortic aneurysm surgery in Denmark, Journal of Medical Economics, 2009, in which we find that the Danish DRG-tariffs did seem to be a fairly good estimate of local cost at Viborg Hospital. The health economic evaluation by Ehlers et al. should be regarded as a scientific contribution to the discussion of the appropriateness of AAA screening from a societal point of view. Our final remark therefore concerns this broader view. A population screening program must be seen as a public health intervention and not as a cardiovascular intervention [5]. The available evidence from the MASS-trial (and similar AAA trials) represent a cardiovascular research tradition. The MASS trial does not include public health issues such as smoking cessation and alternative or complementary life-style interventions. The trial does not entail a proper description of AAA patients including their general well-being, comorbidity, smoking habits, BMI, blood pressure etc. AAA is in most cases a life-style related disease; the prevalence of AAA is 3-6 times higher in smokers and more than 90 % of AAA-patients have a history of smoking [6]. The MASS trial finds an association between AAA death and participation in the AAA screening program but they do no control for life-style issues [5, 7]. The gained life years may be due to other things than surgery such as smoking cessation, life-style changes etc. These confounding issues may in fact explain a large part of the gained life-years, but this has not been investigated. If the MASS trial were to be replicated today the design would probably be different. The result of the Danish cost effectiveness study should be an opportunity to include these aspects in the debate. References 1. Ehlers L, Overvad K, Sørensen J, Christensen S, Bech M, Kjolby MJ. Analysis of cost effectiveness of screening Danish men aged 65 for abdominal aortic aneurysm. BMJ 2009;338:b2243. 2. Drummond M, Schulper MJ, Torrance GW, O'Brian B, Stoddart GL: Methods for the evaluation of health care programmes. Oxford: Medical Publications; 2005. 3. Henriksson M, Lundgren F: Decision-analytical model with lifetime estimation of costs and health outcomes for one-time screening for abdominal aortic aneurysm in 65-year-old men. Br J Surg 2005, 92:976-983. 4. Lindholt JS, Juul S, Fasting H, Henneberg EW: Cost-effectiveness analysis of screening for abdominal aortic aneurysms based on five year results from a randomised hospital based mass screening trial. Eur J Vasc Endovasc Surg 2006, 32:9-15. 5. Medical Advisory Secretariat, Ministry of Health and Long-Term Care: Ultrasound screening for abdominal aortic aneurysm. Health technology policy assessment. Ontario, Canada; 2005. 6. Cronenwett JL, Likosky DS, Russel MT, Eldrup-Jørgensen J, Stanley AC, Nolan BW: A regional registry for quality assurance and improvement: The Vascular Study Group of Northern New England (VSGNNE). J Vasc Surg 2007, 46:1093-1102. 7. Ashton HA, Buxton MJ, Day NE et al. The multicentre aneurysm screening study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002;360:1531-1537. Competing interests: None declared |
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