Burden of disease and costs of aneurysmal subarachnoid haemorrhage (aSAH) in the United Kingdom

Aneurysmal subarachnoid haemorrhage (aSAH) (International Classification of Diseases 10^th revision code I60) is a type of cerebrovascular disease and a main cause of disability and mortality in relatively young patients, with an average age at first onset of 55 [1]. The incidence of aSAH has been estimated at around 6-7 per 100,000 people in most populations [1]. The epidemiology and effectiveness of treatments of aSAH is well-documented in the literature [2] and cost analyses of alternative therapies to treat aSAH are also available [3‐5]. However the overall economic burden of aSAH to society remains unknown.

Making accurate economic estimates of resources associated with particular health problems provides useful information for Departments of Health worldwide [6]. These figures can be used by health care decision makers to understand the overall impact of a disease on the annual health care budget and to provide parameter estimates for economic models, including value of information studies. If performed at regular intervals such studies help to monitor the impact of health care policies as well as changes in clinical practice. For example, in the field of aSAH, the increased use of endovascular intervention with its associated shorter length of stay is likely to influence the total budget, and this may be of interest to decision makers. Detailed comparisons of such health care expenditure estimates across countries may also play a part in assessing the aggregate performance of health care systems [7]. Finally, the results of these studies can provide useful information to communicate the cost burden of a specific disease to a wider non-specialist audience [8].

A recent study has published detailed estimates of the costs of cerebrovascular diseases as part of a study of cardiovascular disease (CVD) related expenditures in the United Kingdom [9]. The authors estimated the annual healthcare costs for cerebrovascular diseases for the UK National Health Service (NHS) to be £5.2 billion and the total economic burden (including non-health care costs) to be £8.5 billion in 2004. aSAH has been estimated to be around 3% of all annual cerebrovascular events in the Oxfordshire region [10]. Although it is tempting to apply this figure to the cerebrovascular disease costs already calculated to estimate the UK costs of aSAH, this could produce seriously flawed results if applied generally: cerebrovascular diseases encompass different types of conditions and it is likely that each of them has different resource use consumption patterns; e.g. length of stay varies across cerebrovascular conditions. As a result, to calculate reliable cost estimates of aSAH we need to undertake a specific cost-of-illness study.

The main objectives of this study were to estimate the economic costs of aSAH in the United Kingdom, including direct healthcare costs, informal care costs and employment-related costs. The number of life-years and quality-adjusted life years (QALYs) lost due to premature death are also reported.

This paper reports the first cost-of-illness analysis of aSAH in the United Kingdom. Aneurysmal subarachnoid haemorrhage cost the NHS £168.2 million in 2005 with overall aSAH-related costs estimated to be £510 million using the human capital and £495 million when using the friction method. This accounts for 6% of the £8.8 billion (2005 prices) for the UK costs of all cerebrovascular diseases reported by Luengo-Fernandez et al in 2004 [9], and so constitutes a significantly greater proportion of total CVD expenditure than of CVD events: Rothwell et al estimated that 3% of CVD events in Oxfordshire from 2002 to 2005 were aSAH [10].

Age and sex-specific life expectancy and quality-adjusted life expectancy for a general population and an aSAH cohort are reported in this study, indicating that aSAH is associated with a loss of 11.1 years of life expectancy and 10.4 quality adjusted years of life expectancy compared to a general population. Quality of life of aSAH patients has also been reported recently in a study using the Short-Form SF-36 but no utility values to derive QALYs were included in this analysis [34]. Therefore to our knowledge no similar estimates, as detailed as the current research, have been reported to date. The SF-36 is a multiattribute generic quality of life outcome widely used by the clinical community [35]. It includes 36 items that can be summarised in eight domains plus a physical and a mental component.

This study estimated the per patient healthcare costs of treating aSAH to be £23,294 per annum. A recent detailed cost study of the UK costs of endovascular and surgical clipping following aSAH has reported that these patients cost the NHS £19,306 (community and social service costs not included in the study) on average during the first year after the collapse [5]. Removing CHSS from the cost estimates presented here, the NHS cost per patient would be £19,107; this is similar to the result reported by the recent UK cost study and supports the figures presented here.

Several limitations of this study need to be highlighted. The community and social service costs extracted from the Burden of Disease Report for this study are becoming out of date [14]. The recent primary care trusts programme budget is beginning to provide more reliable estimates of these cost figures [36]. However, no detailed data on aSAH were available from this new source when performing this study. The characteristics and management of patients in a clinical trial such as ISAT may differ from routine clinical care and hence the parameters used in this study may be subject to some degree of bias. For example, the proportion of patients attending a follow-up angiogram or a rehabilitation programme was extracted from ISAT and therefore refers only to treated aneurysms. The same proportions for untreated aneurysm were not available when conducting this study. However, the sensitivity analysis showed the effect of varying these parameters on the overall costs. Finally, the one-way sensitivity analysis performed ignores any possible covariance across different categories of costs and hence this aspect needs to be considered in future research.

An additional limitation of the current research was the ability to include co-morbidity costs related to aSAH. Aggregate data on finished admissions where aSAH was the primary diagnosis was the main source used in the calculation of the hospital inpatient admission costs and the number of patients with aSAH. If co-morbidities costs are substantial our results may be sensitive to this parameter.

Cost-of-illness studies have been criticised for the variety of methods applied to report their results. This reflects the fact that clear guidelines on how to conduct these analyses are not currently available [37]. This research mainly uses aggregate data coded by specific aSAH diagnosis to minimise the bias of including potential costs not related to the disease. It can be argued that using this type of data from national databases is subject to confounding across health areas. Nevertheless, the type of health care received by aSAH patients is very specific and therefore the impact of confounding on the overall costs estimated is expected to be limited. In addition, cost-of-illness studies are systematically different from traditional methods of economic evaluation and therefore the results from such studies cannot be interpreted in the same manner. This has received some criticism from the health economics community and although this is partly true, cost-of-illness studies provide useful information to prioritise healthcare. Cost-of-illness studies provide information that may be useful to decision makers when identifying priority disease areas for research funding and to develop prevention policies [11]. In addition, these studies provide a framework to evaluate the impact of population changes such as ageing on health outcomes and overall healthcare costs. Finally, the results reported here will provide useful information with which to populate economic models of interventions in the field of aSAH.

The economic and disease burden of aSAH in the United Kingdom is reported in this study. Decision-makers can use these results to complement other information when informing prevention policies in this field and to relate health care expenditures to disease categories. In addition, the results from this study will inform future epidemiological and economic models with useful data on quality of life and costs of patients with aSAH.