Abdominal Aorta Aneurysm Screening

Costs and economic evaluation

Authors: Suvi Mäklin, Taru Haula, Kristian Lampe, Jaana Leipälä, Ulla Saalasti-Koskinen

Summary

The systematic literature review and economic evaluation presented here provide information on the relative costs and cost-effectiveness of population-based abdominal aortic aneurysm (AAA) screening compared with no population-based screening for AAA. The cost-effectiveness analysis was performed from a Finnish healthcare payer perspective and based on recent Finnish clinical practices. The primary investments needed to start a new screening programme and the long-term consequences of possible surgical complications were not taken into account in this analysis.

A total of 26 cost-effectiveness analyses and four systematic reviews on cost-effectiveness were included in the systematic literature review. A positive effect overall over the lifetime of the screened population was observed in all of the included 26 cost-effectiveness analyses. Only a few of the studies included women. The life years gained (LYG) ranged from 0.013 to 0.097 for men and from 0.011 to 0.07 for women. The quality-adjusted life years (QALYs) gained ranged from 0.011 to 0.07 (reported only for men). The incremental cost-effectiveness ratio (ICER) varied across studies, from 157 €/LYG and 179 €/QALY to 43 485 €/QALY. This was to be expected because of differences in the study settings (e.g. healthcare setting, time horizon, included costs, and other modelling assumptions). The cost per LYG/QALY gained was lower than 10 000 € in 23 of the 26 studies. The four systematic reviews were not uniform in their conclusions. Three of the systematic reviews stated that AAA screening for men aged 65 years or older will probably gain additional life years and QALYs at acceptable extra costs but further analysis is needed. One of the reviews stated that most health economic evaluations have made optimistic assumptions in favour of AAA screening and the topic needs further analysis. Our current review contains seven studies that were published after the timelines of the four reviews.

According to our cost-effectiveness analysis, the incremental effectiveness of population-based one-time ultrasound screening for 65-year-old men in Finland would be 0.027 LYG compared with no screening (11.55 vs. 11.52 life years, respectively). The incremental effectiveness for women would be 0.013 LYG (15.69 vs. 15.67 for screening and no screening, respectively). The ICER for one-time screening of 65-year-old men would be 8433 €/LYG compared with no screening. The corresponding ICER for women would be 7198 €/LYG. These results correspond to the majority of the results from other analyses. The results for women should be interpreted with caution due to the limited evidence available for women. Most of the values used in the model for women were from studies concerning men.

In conclusion, currently available evidence and our cost-effectiveness analysis speak for the cost-effectiveness of AAA screening in the male population. Current evidence does not provide justification for excluding women from AAA screening either, but further research is needed on the effectiveness and cost-effectiveness of AAA screening in women.

Introduction

The analysis within the costs and economic evaluation domain aims to provide information about the relative costs and cost-effectiveness of population-based abdominal aortic aneurysm (AAA) screening compared with no population-based screening for AAA of 65-year-old men and women. The aim is to support decision making by comparing costs and outcomes of a technology with its comparator. In publicly funded healthcare systems, finite resources mean that all interventions cannot necessarily be provided in every situation for all who need or demand them. Choices must be made between effective healthcare interventions; the decision to fund one intervention may mean that others cannot be funded {1}.

First, this domain reviews previously published economic evaluations of AAA screening. The systematic review in this domain aims at giving an overview of published economic evaluations of AAA screening, instead of presenting a specific figure of cost-effectiveness based on the literature. We also present all economic evaluations we found, irrespective of their setting and timing. The evidence table (Appendix ECO-2) allows users to find the studies that could be relevant in their country or region, and study those more carefully.

In addition, a cost-effectiveness analysis from a Finnish healthcare payer perspective provides model-based estimates of effectiveness in terms of life years gained (LYG). However, the long-term health impacts and costs of possible surgical complications are excluded from the model. Testing of the model in different settings was beyond the scope of this work. Therefore the model and its results may not be directly applicable in different European settings.

Methodology

Frame

The collection scope is used in this domain.

Assessment elements

Methodology description

Information sources

Systematic literature review

A systematic literature search in CRD, NHS-EED and Medline databases until March 2012 was conducted (Appendix ECO-1) to find published articles on costs and cost-effectiveness of abdominal aortic aneurysm screening.

Cost-effectiveness analysis

Cost-effectiveness analysis was undertaken using a previously constructed model {2}, which was modified to be more in line with the Finnish perspective and clinical practices {3}. The parameters used were based mainly on existing literature, but also on Finnish data and on expert opinion if no other references were available.

Furthermore, a questionnaire sent to EUnetHTA partners in December 2011 (with reminders in 2012) was used to collect information on some of the issues in this domain. (Appendix COL-1)

Quality assessment tools or criteria

In the systematic review, only peer-reviewed cost-effectiveness analyses and systematic reviews of economic evaluations were included. Reviews, letters, comments, etc. were excluded.

The quality of the included studies was not formally assessed. The justification to refrain from formal quality assessment stems from the nature of economic analysis. The aim of economic evaluations, and this domain in a core health technology assessment (HTA), is to aid decision-making. However, the generalisability and transferability of economic evaluations are limited due to their context- and time-specific nature. For a specific context and setting, a systematic review of economic evaluations could be used to identify the most relevant studies to inform a particular decision. Even a high-quality economic study might be highly irrelevant for a particular question, if it focuses on a different kind of healthcare setting with different resources and costs, in a different kind of population, and/or was conducted a long time ago. (See for example Anderson R 2010; {4})

Thus the systematic review in this domain aims to give an overview of published economic evaluations of AAA screening, instead of presenting a specific figure of cost-effectiveness based on the literature. We also present all the economic evaluations found using our search strategy, irrespective of their setting and timing. From the evidence table (Appendix ECO-2) can be found studies that could be relevant in any particular country or region, and the reader is invited to study those more carefully.

Analysis and synthesis

Systematic literature review

A systematic literature search in CRD, NHS-EED and Medline databases until March 2012 was conducted (Appendix ECO-1 ) to find published articles on costs and cost-effectiveness of AAA screening. Full or partial economic evaluations focusing on population-based AAA screening using ultrasound, and systematic reviews about those, were included. Articles were excluded if screening was performed using techniques other than ultrasound (e.g. computed tomography [CT], magnetic resonance imaging [MRI]), or if 64-65-year-old people were not included. Letters, editorials, comments etc. were also excluded. There were no limitations placed on the language of abstracts and articles.

The systematic search strategy for this domain is presented in Appendix ECO-1. After excluding duplicates, 184 abstracts were read independently by two of the authors (TH, KL, SM, USK) and 69 articles were ordered for full-text evaluation. References were taken for full-text evaluation even when only one of the two authors selected it. One additional, study was identified apart from this, as Finohta´s own report on AAA screening {3} did not appear in the literature search. Two of the authors (SM, TH) read full-text articles independently and 30 were included in the review (Figure 1). Twenty-six of the included studies were cost-effectiveness analyses, and four were systematic reviews of economic evaluations. The included articles were summarised in an evidence table (SM, TH) (See Appendix ECO-2), presenting the aims, methods, results and conclusions of the included articles. Meta-analysis was not attempted. Four cost analyses are also presented in the table for information purposes, without analysing them further {5-8}.

Figure 1. Flow chart showing the systematic literature review.

Cost-effectiveness analysis

A cost-effectiveness analysis was conducted from a Finnish healthcare payer perspective using a previously constructed Markov model (Figure 2 and Appendix ECO-3) {2, 3}. The model estimated the cost-effectiveness of one-time ultrasound screening offered to 65-year-old men or women, compared with no population-based AAA screening. The analysis was done separately for men and women. TreeAge Pro HealthCare (version 2011, TreeAge Software Inc.) was used to run the Markov cohort simulation model until all members of the cohort died from AAA-related causes or reached the end of their expected lifetime. Both the estimated future costs and effectiveness were discounted using a 3% discount rate. Probabilistic sensitivity analysis was performed. No health-related quality of life (HRQoL) data were included in the analysis (for HRQoL data, see for example result card RC-SAF1), and the outcomes are reported as LYG and incremental costs per LYG.

The model compared two alternative scenarios (population-based AAA screening vs. current practice, i.e. no population-based AAA screening). These, and the attendance to screening, were modelled in a decision tree and the further years were modelled in a Markov model (Figure 2). The Markov model comprised eight health states: no AAA (<3 cm); small AAA (3-4.4 cm); medium AAA (4.5-5.4 cm), large AAA (>5.5 cm); elective surgery; post-operative state after elective surgery; post-operative-state after emergency surgery; rupture of AAA; and death. The cycle length was one year. If a small or medium AAA is detected in screening, a person is followed-up using ultrasound once a year, and if a large AAA is detected, the person goes into elective surgery (open or endovascular).

The model included some key assumptions. First, it is assumed that if abdominal aorta is found to be normal (<3 cm) during screening, the person will not develop AAA in their remaining lifetime. Secondly, the sensitivity and specificity of ultrasound is assumed to be 100% (see result card RC-SAF3; {9}). Furthermore, the analysis of screening in women is mainly based on epidemiological and effectiveness data from studies on men because of a lack of such data on AAA in women.

Published evidence and national registers were mainly used to inform the model and its input parameters. Expert opinion was used when necessary. The parameter values and distributions used in the sensitivity analysis are presented in Table 1. The parameters related to ‘no population-based AAA screening’ were based on recent data from Finland, as currently no population-based screening for AAA has been implemented. Although the parameter values reported in Table 1 are similar for both arms, differences between the screening arm and the control arm exist as a result of the structure of the model (see Appendix ECO-3). For example, the probability of having elective surgery is similar for all those who have a large AAA detected. In the screening arm, most of the large AAAs are found and thus the number of elective procedures is greater than in the control arm, where only a minority of large AAAs are detected incidentally. And since most of the large AAAs in the screening arm are treated, the number of ruptures is lower than in the control arm. Furthermore, it is assumed that elective surgery is performed before rupture (if the person is eligible for surgery). This part concerning the risk of rupture is the major modification made to the original model by Ehlers et al. {2}.

The number of performed AAA-related surgical procedures, both elective and emergency, was taken from the national Hospital Discharge Register. The age-specific mortality rates for both genders were taken from the registries of Statistics Finland. The number of deaths due to AAA and ruptured AAA (rAAA) were taken from the national Cause of Death Register, and both of these registers were linked in order to estimate the number of deaths after AAA treatment (30 day mortality). Furthermore, it was assumed that long-term survival after elective and emergency surgery was similar to that of the general population and so the age-specific mortality rates were also used for the post-operative states in the model. The cost of invitation to screening was estimated according to the invitation costs of other screening programmes in Finland. Two different costs were estimated for ultrasound as it was assumed that the screening ultrasound would be performed in primary healthcare, and the ultrasound in follow-up would be hospital-based and thus more expensive. The costs of ultrasound and computer tomography were obtained from the hospital district of Helsinki and Uusimaa. The operation costs (elective and emergency) were based on the means of the actual costs of all AAA patients treated in the hospital district of Helsinki and Uusimaa in January-August 2010. The costs of primary investments needed when starting a new screening programme were not included in the analysis.

Figure 2. Structure of the model. Participation in screening is first modelled in a decision tree and then the cohort moves to the Markov model subtree. The Markov states are applicable to all of the three arms (attend screening; invited but do not attend screening; and not offered population-based screening).

Table 1. Parameter values used in the cost-effectiveness analysis.

Result cards

Resource utilization

Unit costs

Outcomes

Cost-effectiveness

Discussion

The present analysis of the cost-effectiveness of AAA screening is based on a combination of a systematic literature review and modelling.

We found four systematic literature reviews with somewhat conflicting conclusions. Our own literature review contains seven studies that were published after the four earlier reviews and hence it contains more recent data. Additionally, we included literature in any language and without time limits. This review is, therefore, likely to contain a more complete overall picture of the effectiveness and cost-effectiveness of AAA screening.

We have not included a systematic analysis of the quality of included studies, since it would have required a substantial amount of extra work and its utility would have remained somewhat controversial. The value of including such an analysis in a core HTA would be a useful discussion topic for the European health economics community.

The primary limitation and challenge in our literature review – as always in the field of health economics – is the limited transferability of results from one setting to another and the difficulty of combining the results in a reliable manner. We have addressed this challenge by including a full cost-effectiveness analysis in the analysis of this domain. Our original intention was to use as much data as possible directly from the other domains, however, many of the analyses in this domain are dependent on the final results and data from other domains. Limited timelines meant that these data were not available within a time frame that would permit analysis. For this reason, and because economic components are generally very context dependent, the analysis is based on data from the Finnish healthcare setting. While the results of this modelling, as such, may not be useful in different settings, the model itself will be made available to researchers from EUnetHTA member organisations. Unfortunately – and due to time and resource limitations – testing of the model in different settings was beyond the scope of this work. Hence we cannot be certain about the applicability of the model in different European settings.

We used a previously constructed model combining a decision-tree and a Markov model {2}, which we modified so that it would better match with clinical practice in Finland. Although the parameter values reported in Table 1 are similar for both arms, differences between the screening arm and the control arm exist as a result of the structure of the model (see Appendix ECO-3). For example, the probability of having elective surgery is similar for all those who have a large AAA detected. In the screening arm, most of the large AAAs are found and thus the number of elective procedures is greater than in the control arm, where only a minority of large AAAs are detected incidentally. And since most of the large AAAs in the screening arm are treated, the number of ruptures is lower than in the control arm. Furthermore, it is assumed that elective surgery is performed before rupture (if the person is eligible for surgery). This part concerning the risk of rupture is the major modification made to the original model by Ehlers et al. {2}. We conclude that this modification is the main explanation for the difference between our results and those of Ehlers et al. {2}.

We found that the ICER of population-based AAA screening in Finland would be 8433€ per life year gained, if ultrasound screening were offered once to 65-year-old men. The ICER for women would be lower, 7198€/LYG, due both to lower incremental costs and lower incremental effectiveness of AAA screening compared with no population-based AAA screening. The results for women should, however, be interpreted with caution as they are heavily based on data for men, and on assumptions that the natural course of AAA is similar in men and women. As is typical for most screening programmes, the largest costs of AAA screening would be manifest immediately at the beginning of the programme whereas the benefits would emerge far into the future. Our analysis has some limitations, for instance it did not include possible long-term consequences (e.g. costs of rehabilitation, decrement in quality of life) after the intervention. Also possible risk groups were not stratified but all patients were assumed to have the same risk for AAA.

Our results of the cost-effectiveness of AAA screening are not directly transferable to other healthcare systems (this can be seen e.g. on the unit cost card, ECO3). An important limitation of our assessment should be noted here: There have not been any local pilots or feasibility studies on AAA screening in Finland. Thus we had to base our assessment on a totally hypothetical perception of how the screening would be organised in Finland. Hence we refrained from including any primary investment costs for the screening in our modelling, for these costs would have been highly hypothetical in nature. If reliable information on the primary investment costs were available for instance from a local trial or pilot programme, including them in the model would of course improve the accuracy of the economic evaluation of the screening.

A major economic and organisational consequence of starting AAA screening would be a significant increase in the number of elective operations compared with the situation when screening is not offered. In Finland offering AAA screening to 65-year-old men, would more than double the number of these operations, and offering the screening also to 65-year-old women, these operations would triple in number. If the screening were to be started without sufficient resources for the operations, the treatment of other conditions needing vascular surgery could be endangered.

When deciding whether to start AAA or any screening, the question of prioritisation criteria may also arise. Such criteria have not been defined in Finland and to our knowledge not in most (if not all) European countries either. When considering AAA screening, especially the fact that it would prevent AAA-related deaths in a rather aged population might generate debate (the median age of a death due to AAA is 77 years in Finland). Furthermore, one could ask whether the effectiveness of screening compared with other preventive or health-promoting measures should be considered? For example: how effective is AAA screening compared with anti-smoking education in preventing AAA-related mortality?

In conclusion, the majority of the available evidence as well as our present evaluation suggest that one-time ultrasound screening for AAA of 65-year-old men and women is cost-effective compared with a situation where no AAA screening is offered. There is, however, only scarce evidence on AAA screening in women, and further research regarding women is needed.

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Appendices

Appendix ECO-1 Literature search strategy.

Appendix ECO-2 Evidence table.

Appendix ECO-3 Structure of the model.