Abstract
Background and Purpose
Few studies have evaluated long-term costs after stroke onset, with almost no cost data for TIA. We studied hospital costs during the 5 years after TIA or stroke in a population-based study.
Methods
Patients from a UK population-based cohort study (Oxford Vascular Study) were recruited from 2002 to 2007. Analysis was based on follow-up until 2010. Hospital resource usage was obtained from patients’ hospital records and valued using 2008/09 unit costs. As not all patients had full 5-year follow-up, we used non-parametric censoring techniques.
Results
Among 485 TIA and 729 stroke patients ascertained and included, mean censor-adjusted 5-year hospital costs after index stroke were $25,741 (95% CI: 23,659-27,914), with costs varying considerably by severity: $21,134 after minor stroke, $33,119 after moderate stroke, and $28,552 after severe stroke. For the 239 surviving stroke patients who had reached final follow-up, mean costs were $24,383 (20,156-28,595), with over half of costs ($12,972) being incurred in the first year after the event. After index TIA, the mean censor-adjusted 5-year costs were $18,091 (15,947-20,258). A multivariate analysis showed that event severity, recurrent stroke and coronary events after the index event were independent predictors of 5-year costs. Differences by stroke subtype were mostly explained by stroke severity and subsequent events.
Conclusions
Long-term hospital costs after TIA and stroke are considerable, but are mainly incurred over the first year after the index event. Event severity and suffering subsequent stroke and coronary events after the index event accounted for much of the increase in costs.
Keywords: Stroke, Transient Ischemic Attacks, Costs and cost analysis
Subject codes: [13] Cerebrovascular disease/stroke, [81] Transient Ischemic Attacks, [100] Health policy and outcome research
Introduction
Cerebrovascular diseases are a leading cause of worldwide deaths,1 and one of the principal causes of hospital and care-home resource utilisation.2 There is therefore much research interest in quantifying the cost of cerebrovascular diseases, and stroke in particular.
Although numerous studies have been published assessing the hospital care costs of stroke using patient-level data, very few studies have evaluated costs for more than one year after stroke onset, with an almost complete lack of long-term hospital cost data for Transient Ischaemic Attack (TIA).2–6 This lack of evidence on the level and predictors of long-term hospital costs following TIA and stroke does not allow for formal comparisons of outcome and cost between these conditions and other diseases, hampering and limiting decisions about the relative funding requirements for service provision and research.7,8 In addition, estimates of long-term disease costs are valuable to other researchers, particularly as an input to decision-analytic models, which are becoming ever more popular to assess the cost-effectiveness of health care interventions.
To reliably determine the level and predictors of resource use and costs after TIA and stroke, population-based studies with full case ascertainment (i.e. including minor events not admitted to the hospital and strokes resulting in death before, or soon after, hospital admission) are ideally required.9 We therefore studied hospital care costs during the 5 years after any first incident or recurrent TIA or stroke in a population-based study.
Methods
The Oxford Vascular Study
The OXVASC study population comprises over 91,000 patients registered in 9 general practices across Oxfordshire, UK. The study methods have been described elsewhere.10 Briefly, patient registration began on April 2002 and is ongoing. Only consenting patients recruited from 1 April 2002 to 31 March 2007 were included in this analysis. Patients in whom TIA or stroke was suspected were ascertained using multiple overlapping methods of “hot” and “cold” pursuit and considered for inclusion,11 including:
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1)
A daily (weekdays only), urgent open-access “TIA clinic” to which participating general practitioners (GPs) and the local accident and emergency department (A&E) send all individuals with suspected TIA or stroke whom they would not normally admit to hospital, with alternative on-call review provision at weekends;
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2)
Daily searches of admissions to the medical, stroke, neurology and other relevant wards;
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3)
Daily searches of the local A&E attendance register;
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4)
Monthly computerized searches of GP diagnostic coding and hospital discharge codes;
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5)
Monthly searches of all cranial and carotid imaging studies performed in local hospitals; and
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6)
Monthly reviews of all death certificates and coroners reports.
Suspected TIA/stroke patients were assessed urgently by a study clinician. Stroke was defined according to World Health Organisation (WHO) definitions and included all ischaemic events, intracerebral haemorrhage (ICH), subarachnoid haemorrhage (SAH), and strokes of uncertain type. Informed consent was sought, and assessments of neurological impairment, history of presentation, medical and social history, and risk factors were performed. Impairment was measured using the National Institutes of Health Stroke Scale (NIHSS), which was used to categorise event severity. Minor events were defined as NIHSS scores<3, moderate as scores from 4 to 10, and severe as scores>10. Although different study physicians were involved during the study, all cases were subsequently reviewed by the study senior neurologist (PMR) on a daily basis and imaging results were assessed by the same neuroradiologist, with the final classification as TIA, stroke or other condition being made by the same senior neurologist and neuroradiologist in all cases.
Surviving patients were then followed-up face-to-face by a research nurse at 1, 6, 12, 24 and 60 months after the event. Patients were also followed-up via their GP and hospital records, recurrent vascular events were identified by ongoing ascertainment, and all patients had mortality follow-up.
Resource use and unit costs
Resource use was obtained from patients’ hospital records from the date of first TIA or stroke within the OXVASC study period (i.e. index event) until 31 March 2010. In addition, resources used within the year prior to the index event were obtained. For those patients recruited before 1 April 2005, only resource use up to 5 years after the event was collected. Minimum follow-up in the study was 3 years.
Patients’ hospital records from the Oxford Radcliffe Hospitals NHS Trust (at the start of OXVASC it comprised one tertiary hospital, 3 acute general hospitals and 9 community hospitals) were reviewed for any accident & emergency (A&E) visit, emergency transport, outpatient care visit, day case or hospitalisation. For each spell in hospital, information was recorded on the date of admission and discharge and the dates of transfers between different specialty wards. Hospitalisations in which patients were admitted and discharged on the same day were classified as day cases and the number of days in hospital was set to 0. Inpatient stays were defined as those spells in which the patient was admitted for at least one night. Although it would have been ideal to report hospitalisations, days in hospital and costs separately for acute care and rehabilitation care, in most UK hospitals, acute care and rehabilitation are less separable than in the USA or other European models. In the UK, rehabilitation is generally initiated on the stroke unit, or general ward, with some patients staying for several weeks and/or admitted into specialist rehabilitation wards or community hospitals subsequently.
Regardless of when hospital resources were consumed by patients, all resource use was priced using 2008/09 unit costs. When unit costs were obtained from sources detailing costs before 2008/09, costs were updated using the Hospital and Community Health Services pay and price inflation index.12 Unit costs for outpatient (including any outpatient investigations performed) and A&E visits were derived from the schedule of reference costs for NHS trusts.13 For each hospital ward, the unit costs per day case/day in hospital were derived from the schedule of NHS reference costs,13 and NHS trust financial returns.14 The only exception was for the cost per day in a stroke unit, which was derived from published studies due to lack of data in NHS published costs.15 The unit costs employed to price inpatient resource use also included the costs of treatments, investigations and interventions typically performed in each specialty ward. All costs were converted from UK pounds sterling (£) to US dollars ($).The currency conversion was based on the rate of purchasing power parities in 2009 ($1 is equal to £0.64).16
Costs incurred by patients after the first year have not been discounted to present value terms in the main analysis. However, sensitivity analyses are presented in which costs incurred after the first year were discounted using a 3.0%, 3.5% and 5.0% annual rate to reflect the different discount rates used in different countries.
Statistical analysis
Resource use data up to 31 March 2010 were used; therefore, we did not have full 5-year data for patients recruited after 1 April 2005. As a result cost results are presented for those with full follow-up (including those dying within that time - complete case analysis), and for the whole patient sample after adjusting for censoring.
We examined the effect of censoring on our results using the method developed by Lin et al.17 This method partitions the study period into smaller time periods (in this case by day) within each of which the total cost incurred for all patients alive at the beginning of the period is calculated. The estimated costs of patients with complete data for each time period are then weighted by the Kaplan Meier sample average estimator (i.e. the probability of survival in a given time period, conditional on having survived the previous time period), and summed over all periods to obtain an estimate of the mean censor-adjusted costs. Costs are reported as means together with their 95% confidence intervals (CI). 95% CIs are reported around the mean censor-adjusted costs using 1000 bootstrap estimates.
As TIA and stroke are associated with old age and generally occur in patients with other co-morbidities,10 such patients are likely to consume substantial hospital resources even if they had not suffered a TIA or stroke, making the impact of disease on costs difficult to determine. Therefore, we also compared the costs for each of the 5 years after the index event with the costs incurred before the event by undertaking two analyses: 1) surviving cases – in which annual costs before and after the index event were compared only for patients who survived past 5 years; and 2) available cases – in which annual costs before and after the index event were compared by estimating the mean annual cost for patients, including cases who died, with complete data for that year.
To assess if the predictors of hospital care costs varied over time, two log-linear regression models, using robust standard errors, were employed to assess the predictors of 1- and 5-year total hospital care costs after TIA or stroke.18 For the analysis of 5-year costs only patients with full 5-year follow-up were included, and to make results directly comparable the same patients were included in the analysis of costs incurred from index event to 1 year. Predictors of costs included were: age; gender; previous history of each of myocardial infarction, angina, peripheral vascular disease (PVD), hypertension, stroke, atrial fibrillation or diabetes; event type (TIA or stroke); event severity (NIHSS score); disability before the event; any subsequent vascular event at 1 and 5 years after index TIA or stroke; living arrangements before the index event; marital status; socio-economic status; employment status; and deprivation as measured using the index of multiple deprivation. Due to observed non-linear effects on costs,15 event severity was included in the model using the continuous NIHSS score and its quadratic term. Age was included as a categorical variable. In order to assess the impact of individual patient characteristics on costs, after covariate adjustment, we estimated the difference between mean predictions using appropriate smearing estimators.19 Similar regression models were undertaken only for stroke patients including as an additional covariate stroke subtype using the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification.
Statistical significance was set at p<0.050. Model specification was tested using Ramsey’s reset test - a general specification test for the linear regression model used to test whether non-linear combinations of the fitted values helped explain 5-year costs. In order to assess whether the results from the linear regression were valid, we also assessed whether the residuals were normally distributed and if there were any patterns in the residuals when plotted against the predicted values.
Results
Patient sample
Between April 2002 and March 2007, 485 patients had a TIA and 729 patients a stroke as their index OXVASC event. Mean age of the sample was 75 (S.D. 13) years for stroke patients and 73 (S.D. 13) for TIA patients. Males accounted for 51% (n=369) of stroke cases and 44% (n=211) of TIA cases (Table 1). There was missing NIHSS information for 17 stroke cases, due to late presentation or events occurring out of area. Of the 712 index strokes with available NIHSS scores, 413 (58%) were classified as minor, 166 (23%) as moderate, and 133 (19%) as severe.
Table 1. Baseline characteristics.
| Stroke (n=729) | TIA (n=485) | |
|---|---|---|
| Mean age (years), mean (S.D) | 75 (13) | 73 (13) |
| Males | 369 (51) | 211 (44) |
| Previous myocardial infarction* | 98 (14) | 54 (11) |
| Previous angina* | 118 (16) | 77 (16) |
| Hypertension* | 437 (61) | 251 (52) |
| Previous stroke* | 135 (19) | 53 (11) |
| Diabetes* | 76 (11) | 65 (13) |
| Previous disability: | 151 (21) | 70 (14) |
| NIHSS score†, median (IQR) | 3 (1 to 7) | 0 |
| Minor stroke | 413 (58) | |
| Moderate stroke | 166 (23) | |
| Severe stroke | 133 (19) | |
| TOAST classification: | ||
| Cardioembolism | 182 (25) | |
| Large artery atherosclerosis | 53 (7) | |
| Small vessel occlusion | 109 (15) | |
| Other determined aetiology | 7 (1) | |
| Undetermined/unknown aetiology | 273 (37) | |
| Multiple possible aetiologies | 12 (2) | |
| Primary intracerebral haemorrhage | 54 (7) | |
| Subarachnoid haemorrhage | 39 (5) |
Data expressed as n (%), except where specified. IQR – Interquartile range
Stroke: 7 missing; TIA: 2 missing
Stroke: 17 missing; TIA: 5 missing
Of the 729 patients suffering an index stroke, 239 (33%) were alive at 5 years, 333 (46%) had died within that time, and 157 (22%) had not yet reached full 5-year follow-up (online supplementary material - Table S1). 204 (42%) index TIA cases were alive at 5 years, 25% (n=120) had died, and 161 (33%) patients had not yet reached full 5-year follow-up. Mean censor-adjusted survival time was 4.32 years after TIA and 3.30 years after stroke. Of the 729 stroke patients, 144 (20%) suffered one or more recurrent strokes and 60 (8%) suffered one or more subsequent coronary events during the five 5-year follow-up. 107 (22%) TIA patients suffered one or more strokes and 51 (11%) suffered one or more coronary events following index TIA.
Details of hospital care resource use after index TIA and stroke are reported in the online supplementary material (Table S2).
5-year hospital costs after stroke
For the 572 stroke patients with full 5-year follow-up, or dying within that period, the mean 5-year-total hospital costs after stroke were $26,475 (95% CI: 23,723 to 29,227), of which $23,397 (88%) were due to inpatient stays in hospital (Table 2). Whilst minor stroke patients (NIHSS score ≤3) incurred average costs of $23,031 (19,616 to 26,448), moderate stroke patients (NIHSS score 4 to 10) incurred costs of $31,953 (25,784 to 38,120). Despite high mortality rates after severe stroke (NIHSS score >10), with mean survival time of 1.45 years, these patients still incurred average costs of $27,348 (21,085 to 33,617).
Table 2. 5-year mean hospital care costs ($, 95% CI) after index event.
| No. | Emergency transport | Accident & Emergency | Day cases | Inpatient stays | Outpatient visits | Total costs | |
|---|---|---|---|---|---|---|---|
| TIA | |||||||
| 5 years – complete cases | 324 | 417 (344-492) | 205 (173-236) | 947 (686-1,208) | 15,689 (12,658-18,722) | 2,128 (1,931-2,325) | 19,388 (16,244-22,531) |
| 5 years – censor-adjusted | 485 | 400 (348-453) | 200 (180-222) | 1,161 (928-1,413) | 14,105 (12,183-16,233) | 2,225 (2,092-2,373) | 18,091 (15,947-20,258) |
| All stroke | |||||||
| 5 years – complete cases | 572 | 483 (430-536) | 209 (188-231) | 773 (630-919) | 23,397 (20,728-26,067) | 1,611 (1,420-1,803) | 26,475 (23,723-29,227) |
| 5 years – censor-adjusted | 729 | 483 (442-528) | 214 (197-231) | 842 (739-966) | 22,511 (20,709-24,711) | 1,691 (1,566-1,830) | 25,741 (23,659-27,914) |
| Mean costs by stroke severity | |||||||
| Minor stroke | |||||||
| 5 years – complete cases | 293 | 456 (381-531) | 208 (178-239) | 1,025 (814-1,236) | 19,200 (15,905-22,495) | 2,142 (1,848-2,436) | 23,031 (19,616-26,448) |
| 5 years – censor-adjusted | 413 | 442 (389-475) | 206 (184-227) | 1,031 (889-1,175) | 17,381 (14,939-19,545) | 2,073 (1,902-2,270) | 21,134 (18,692-24,697) |
| Moderate stroke | |||||||
| 5 years – complete cases | 139 | 555 (430-680) | 236 (183-289) | 722 (380-1,066) | 29,139 (23,183-35,095) | 1,302 (1,005-1,597) | 31,953 (25,784-38,120) |
| 5 years – censor-adjusted | 166 | 580 (478-649) | 250 (208-298) | 841 (605-1,133) | 29,930 (25,342-34,759) | 1,519 (1,297-1,761) | 33,119 (28,322-37,891) |
| Severe stroke | |||||||
| 5 years – complete cases | 127 | 494 (403-586) | 194 (158-230) | 164 (78-250) | 25,738 (15,667-31,810) | 758 (388-1,130) | 27,348 (21,085-33,617) |
| 5 years – censor-adjusted | 133 | 529 (436-589) | 202 (173-233) | 148 (88-225) | 26,902 (22,066-31,983) | 791 (513-1,094) | 28,552 (23,825-33,911) |
| Mean costs by stroke type | |||||||
| Ischaemic stroke | |||||||
| 5 years – complete cases | 467 | 514 (450-577) | 223 (198-250) | 848 (681-1,016) | 24,780 (21,767-27,792) | 1,806 (1,588-2,027) | 28,173 (25,081-31,267) |
| 5 years – censor-adjusted | 599 | 502 (459-552) | 223 (206-242) | 914 (797-1,038) | 22,848 (20,741-25,173) | 1,859 (1,705-2,019) | 26,347 (24,345-28,602) |
| Primary intracerebral haemorrhage | |||||||
| 5 years – complete cases | 40 | 367 (266-470) | 148 (109-186) | 330 (111-548) | 12,941 (5,961-19,919) | 477 (30-923) | 14,263 (6,983-21,541) |
| 5 years – censor-adjusted | 54 | 377 (297-467) | 158 (125-191) | 275 (141-428) | 18,103 (12,603-24,428) | 728 (455-1,055) | 19,641 (13,814-26,136) |
| Subarachnoid haemorrhage | |||||||
| 5 years – complete cases | 33 | 380 (261-500) | 164 (116-213) | 500 (141-861) | 26,766 (13,622-39,911) | 1,248 (450-2,047) | 29,059 (15,417-42,702) |
| 5 years – censor-adjusted | 39 | 384 (302-475) | 163 (130-200) | 605 (341-917) | 31,298 (23,325-42,314) | 1,259 (725-1,850) | 33,708 (23,833-44,661) |
| Unknown stroke | |||||||
| 5 years – complete cases | 32 | 284 (155-413) | 117 (59-177) | 519 (2-1,231) | 12,823 (3,656-21,989) | 548 (123-973) | 14,292 (4,733-23,853) |
| 5 years – censor-adjusted | 37 | 414 (188-734) | 178 (81-308) | 709 (250-1,289) | 12,980 (6,973-19,847) | 786 (461-1,130) | 15,069 (8,544-23,441) |
ANOVA test for differences in total costs: 1) TIA vs. stroke: p=0.001; 2) Stroke severity groups: p=0.029; 3) Stroke type: p=0.012.
To obtain the 5-year average cost for all 729 strokes we adjusted costs to account for censoring. The resulting mean 5-year costs were $25,741 (23,659 to 27,914), which were similar to those obtained in the complete-case analysis (Table 2). Due to high case fatality rates shortly after unknown stroke and primary intracerebral haemorrhage, censor-adjusted 5 year costs were lower than those for ischaemic stroke $15,069, $19,641 and $26,347, respectively), with those for subarachnoid haemorrhage being $33,708. More detailed cost results by TOAST classification are reported in Table 3. The online supplementary material (Table S3) reports all hospital care costs in present value terms, in which costs incurred after the first year were discounted using an annual rate of 3.0%, 3.5% and 5.0%.
Table 3. 5-year hospital care costs after index stroke, by TOAST classification.
| Complete cases | Censor-adjusted | |||
|---|---|---|---|---|
| No. | Mean costs, $ (95% CI) | No. | Mean costs, $ (95% CI) | |
| Cardioembolism | 158 | 30,086 (24,778-35,395) | 182 | 30,175 (26,003-34,416) |
| Large artery atherosclerosis | 39 | 25,708 (15,778-35,638) | 53 | 24,941 (18,092-32,241) |
| Small vessel occlusion | 88 | 28,084 (19,931-36,236) | 109 | 26,872 (21,316-32,709) |
| Other determined aetiology | 5 | 18,209 (4,947-31,472) | 7 | 16,725 (11,570-21,997) |
| Undetermined/unknown aetiology | 200 | 25,000 (20,433-29,566) | 273 | 22,570 (19,453-25,873) |
| Multiple possible aetiologies | 9 | 32,883 (11,564-54,202) | 12 | 28,863 (16,703-41,733) |
| Primary intracerebral haemorrhage | 40 | 14,263 (6,983-21,541) | 54 | 19,641 (13,814-26,136) |
| Subarachnoid haemorrhage | 33 | 29,059 (15,417-42,702) | 39 | 33,708 (23,833-44,661) |
ANOVA test for differences in costs by stroke subtype: p=0.0005
For the 239 stroke patients with full follow-up and who survived the 5 years, the mean 5-year hospital costs were $24,383 (20,156 to 28,595). Over half of these costs ($12,972) were incurred during the first year after stroke, with costs then falling to $2,303 in year 2, $3,486 in year 3, $2,527 in year 4, and $3,088 in year 5. Mean annual costs for each follow-up year after index stroke were significantly higher than those incurred in the year before the event ($923; p<0.001 – Figure 1). Mean costs in the year before the index stroke were significantly higher for patients dying within 5-years after stroke (n=333, $6,205) than for those who survived (n=239, $923; p<0.0001). For all stroke patients, mean annual costs before the index stroke were $3,561, compared with $16,444 in the first year after the index stroke (p<0.001), $2,311 in year 2 (p=0.018), $2,659 in year 3 (p=0.117), $2,106 in year 4 (p=0.007) and $1,952 in year 5 (p=0.006).
Figure 1. Costs before and after index stroke.
*Annual costs before and after the index stroke were compared by estimating the mean annual cost for patients, including cases who died, with complete data for that year.
5-year costs after TIA
For the 324 TIA patients with full 5-year follow-up, or dying within that period, the mean 5-year-total hospital costs after TIA were $19,388 (16,244 to 22,531), of which $15,689 (81%) were due to inpatient stays in hospital (Table 3). Mean 5-year censor-adjusted costs were $18,091 (15,947 to 20,258).
For the 204 surviving TIA patients with full follow-up, the mean 5-year hospital costs were $13,682 (10,558 to 16,809). For these patients, over half of costs ($5,719) were incurred during the first year after TIA, with costs then falling in subsequent years. Although mean annual costs were higher at each follow-up year than in the year before the index TIA, statistically significant differences were only identified for the first and second year after the event (Figure 2). For all TIA patients, mean annual costs before the index stroke were $2,178, with costs remaining higher during the first year after TIA ($6,909; p<0.001), year 2 ($4,420; p<0.001) and year 3 ($2,805; p=0.247).
Figure 2. Costs before and after index TIA.
*Annual costs before and after the index event were compared by estimating the mean annual cost for patients, including cases who died, with complete data for that year.
Predictors of 1- and 5-year costs after TIA or stroke
Log-linear regressions were performed to assess the main independent predictors of 1- and 5-year hospital costs after TIA or stroke. For both analyses we only included patients with full 5-year follow-up (n=896 – including those who died within that period), of whom 140 (16%) were excluded due to missing socio-economic characteristics, leaving a sample of 756 patients. Results are reported in Table 4. Mean predicted costs after covariate adjustment are presented here for significant variables. Year in which the patient was recruited into OXVASC was not included as a covariate in the regression as we found no statistically significant evidence that costs varied between years (ANOVA test for differences in costs by year of recruitment: p=0.444 for TIA and p=0.807 for stroke).
Table 4. Predictors of 1- and 5-year hospital care costs after index TIA or stroke.
| 1-year costs (log transformed) |
5-year costs (log transformed) |
|||
|---|---|---|---|---|
| Coef. | p>|z| | Coef. | p>|z| | |
| Gender | ||||
| Female | Reference case | Reference case | ||
| Male | 0.14 | 0.274 | -0.01 | 0.924 |
| Age, years | ||||
| <65 | -0.14 | 0.531 | -0.51 | 0.003 |
| 65-74 | -0.10 | 0.466 | -0.18 | 0.146 |
| ≥75 | Reference case | Reference case | ||
| Previous history of: | ||||
| TIA | -0.04 | 0.815 | -0.05 | 0.747 |
| Stroke | 0.13 | 0.356 | 0.32 | 0.011 |
| Peripheral vascular disease | 0.35 | 0.066 | 0.26 | 0.137 |
| Myocardial infarction | 0.31 | 0.060 | -0.04 | 0.775 |
| Angina | -0.09 | 0.545 | -0.02 | 0.867 |
| Hypertension | -0.16 | 0.167 | -0.17 | 0.085 |
| Atrial fibrillation | 0.28 | 0.030 | 0.09 | 0.476 |
| Disability | 0.20 | 0.228 | -0.02 | 0.908 |
| Event type | ||||
| TIA | Reference case | Reference case | ||
| Stroke | 0.39 | 0.007 | 0.16 | 0.195 |
| NIHSS score | 0.20 | <0.001 | 0.13 | <0.001 |
| NIHSS score ^ 2* | -0.006 | <0.001 | -0.005 | <0.001 |
| Subsequent events: | ||||
| Stroke | 0.69 | <0.001 | 0.43 | <0.001 |
| Coronary | 1.16 | <0.001 | 0.54 | <0.001 |
| Peripheral vascular | 0.92 | 0.103 | 0.67 | 0.081 |
| Pre-morbid place of residence | ||||
| Own home | Reference case | Reference case | ||
| Home friend/family | 0.01 | 0.976 | -0.33 | 0.346 |
| Warden accommodation | 0.26 | 0.342 | 0.55 | 0.009 |
| Care home | -0.97 | 0.072 | -1.57 | 0.002 |
| Lived alone before event | 0.38 | 0.036 | 0.06 | 0.718 |
| Pre-morbid marital status | ||||
| Married | Reference case | Reference case | ||
| Widowed | -0.03 | 0.882 | 0.06 | 0.757 |
| Single | 0.51 | 0.066 | 0.55 | 0.041 |
| Separated | 0.13 | 0.637 | 0.02 | 0.946 |
| Living with partner | -0.17 | 0.736 | 0.06 | 0.822 |
| Pre-morbid employment status | ||||
| Full-time | -0.12 | 0.611 | -0.04 | 0.820 |
| Part-time | -0.04 | 0.872 | 0.15 | 0.472 |
| Caring for home | 0.03 | 0.935 | -0.01 | 0.982 |
| Unemployed | -0.95 | 0.376 | -0.44 | 0.300 |
| Unable-work | 0.65 | 0.088 | 0.16 | 0.632 |
| Retired | Reference case | Reference case | ||
| Socio-economic status | ||||
| Professional | -0.13 | 0.626 | 0.22 | 0.362 |
| Managerial | -0.03 | 0.847 | 0.04 | 0.788 |
| Skilled non-manual | -0.06 | 0.749 | -0.12 | 0.478 |
| Skilled manual | Reference case | Reference case | ||
| Partly skilled | -0.17 | 0.411 | -0.04 | 0.828 |
| Non-skilled | 0.03 | 0.881 | 0.29 | 0.082 |
| Age left education | -0.02 | 0.150 | -0.04 | 0.046 |
| Index of multiple deprivation | 0.001 | 0.951 | 0.003 | 0.637 |
| Constant | 0.72 | <0.001 | 9.02 | <0.001 |
| No. | 756 | No. | 756 | |
| p>F | <0.001 | p>F | <0.001 | |
| Adj R2 | 0.241 | Adj R2 | 0.175 | |
*The non-linear association between event severity and costs was further tested by including an interaction term between severity and case-fatality (defined as mortality within 30 days of event) into the regression. We found this to be statistically significant, although the non-linear relationship between cost and severity still held.
Event severity was both a strong independent predictor of costs at 1 and 5 years after the index event, with a 1 point rise in NIHSS score increasing 1-year costs by 20% and 5-year costs by 13% (p<0.001 – Table 4). The association between event severity and costs was non-linear, due to the greatly increased case-fatality, and corresponding reductions in health use, observed at high NIHSS scores. This was further tested by including an interaction term between NIHSS score and case-fatality (defined as mortality within 30 days of event) into the regression. We found this to be statistically significant, although the non-linear relationship between cost and severity still held. Although having a history of stroke prior to the index event was not a predictor of 1-year costs, patients with a history of stroke incurred significantly higher costs than those with no history 5 years after the event ($11,973; p=0.011).
One year after the index event stroke patients incurred significantly higher costs of $7,931, after covariate adjustment, when compared with TIA patients (p=0.007). However, 5 years after the index event, the difference in costs between stroke and TIA patients was considerably lower and non-significant ($5,198; p=0.195). Results of the multivariate analysis also showed that, excepting whether the patient was living alone before the index event, only clinical factors were predictors of costs one year after the event, with age and pre-morbid place of residence, marital status and education levels all found to be predictors of 5-year costs. Age was a predictor of 5-year costs, with patients aged less than 65 years incurring $15,172 lower costs than those aged over 75 years (p=0.003, Table 4). Place of residence before the index event was also a predictor of 5-year costs after TIA or stroke. Compared to those living at home before the index event, patients living in nursing homes incurred lower hospital care costs (-$26,722; p=0.002), due to high fatality rates, and those living in warden/sheltered accommodation incurred significantly higher costs $24,461; p=0.009). Education levels were also an independent predictor of costs, with each additional year of education reducing costs by 4% (p=0.046). After controlling for patient characteristics, single patients incurred significantly higher costs ($23,459; p=0.041) than married patients.
Additional regression models, similar to those reported above, were undertaken only for stroke patients including as an additional covariate stroke subtype using TOAST classification definitions. Results from this showed that stroke severity (as measured using NIHSS score) and recurrent strokes and subsequent peripheral vascular events remained the strongest predictors of 5-year hospital care costs. Although significant differences in 5-year costs were identified, univariately, by stroke subtype (Table 3), much of these differences disappeared after controlling for severity, age and other covariates in the regression analysis (online supplementary material, Table S4).
Discussion
A previous OXVASC study assessed the levels and predictors of acute hospital usage and costs after stroke onset.15 This study supplements the previous findings by evaluating hospital care costs after TIA and stroke over the longer term, and is the first population-based study to estimate such costs of TIA and stroke in the UK. To our knowledge the only previous population-based study, using multiple ascertainment methods, of the long-term cost of adult stroke was done in Melbourne, Australia, in a different healthcare system with higher rates of hospital admission, and considering only the costs of stroke.3 A study conducted in Finland, based on 94,316 hospital-treated patients with incident stroke,5 also assessed 5-year costs after stroke and compared these to costs incurred one year before the incident stroke. Ours is also the first study to evaluate long-term hospital costs after TIA, and compare these to pre-event costs.
Our study showed that costs after index stroke and TIA are considerable, with patients incurring 5-year hospital care costs of $25,741 and $18,091, respectively, with the long-term time perspective adopted in this study allowing us to compare the costs incurred at each follow-up year. For stroke patients, 64% ($16,444) of these 5-year costs were incurred during the year immediately after the stroke, whereas for TIA patients, only 38% ($6,909) of 5-year costs were incurred during the first year. As a result, and partly through increased mortality rates in stroke patients, the significant difference in 1-year costs observed between stroke and TIA patients, after adjustment for other covariates, was no longer identified at 5 years.
Another important difference identified between the multivariate analyses of 1- and 5-year costs, was that at 1-year after the index event, the only predictors of costs were clinical in nature, whereas at 5 years, age and social history (including education levels, marital status, and place of residence) were all found to be predictors of hospital care costs. The finding that educational attainment (measured by the age patients’ left education) was associated with 5-year hospital costs could be explained (at least partly) by the strong relationship between education, income and health.20 However, as this finding verged on non-significance (p=0.046), this observed relationship in our study should be treated with caution.
The results of our multivariate analyses also showed that the main determinants of 1- and 5-year hospital costs was the severity of the neurologic deficit (NIHSS score) at initial assessment, and the impact of subsequent strokes or coronary events after index TIA or stroke. Patients suffering subsequent strokes or coronary events were found to incur additional 5-year costs, after controlling for other characteristics, of $15,990 and $22,592, respectively.
As TIA and stroke are associated with old age and often occur in patients with other comorbidities,10 such patients are likely to consume substantial health care resources regardless of event onset. Therefore, to better understand the impact of TIA and stroke on costs, we compared the costs for each of the 5 years after the index event with the costs incurred before the event. As identified in previous studies,21,22 both for TIA and stroke, costs gradually rose over the year prior to the event as patients required more medical attention, suggesting that health deteriorated in the months shortly before the event in some patients.
Although our study shows that a great proportion of 5-year total costs were incurred shortly after stroke, the long-term time perspective adopted in this study also allowed us to compare the costs incurred at each follow-up year with those incurred in the year before the stroke. For stroke patients surviving the whole 5-year period, annual hospital costs after stroke were significantly higher than those before stroke, although costs incurred in the first year after stroke accounted for over half of all 5-year costs. However, when all stroke patients were considered, only one-year costs were significantly higher than those incurred before the event. This finding was due to average annual costs after stroke being pushed down by death, and because the 333 stroke patients who died during the 5-year follow-up had significantly higher costs in the year before the event than those patients surviving past 5 years, pushing-up average annual costs before the stroke.
Population-based cohort studies, such as OXVASC, are the “gold-standard” when evaluating outcomes after TIA and stroke.9 However, our study also had limitations. Firstly, 33% and 22% of TIA and stroke patients, respectively, did not yet have full five-year follow-up and were therefore treated as censored. However, we presented average long-term hospital costs for patients with complete data and after censor-adjustment using recommended techniques. Secondly, the study omitted other relevant healthcare costs such as those relating to primary care visits or community care. However, previous studies have shown that the vast majority of healthcare costs after stroke are due to hospitalisations, with the impact of other cost categories having a relatively small impact on total costs.2 Related to this we omitted the costs of long-term institutionalisation in either nursing or residential home care. Although not a healthcare cost, long-term institutionalisation has been shown to be a major component of overall costs after stroke.4 Third, our overall costs are only applicable to the United Kingdom and possibly to similar healthcare systems in which a high proportion of patients with TIA and minor stroke are investigated and treated in the outpatient setting. Our predictors of cost, however, are more likely to be generalisable to other healthcare settings.
In summary, our study reports estimates of the long-term levels and predictors of hospital care costs associated with stroke in the United Kingdom using data from a well-conducted population-based study. Our results highlight the importance of initial stroke severity as a predictor of costs. This study should be of use to analysts assessing the burden of TIA and stroke and the long-term cost-effectiveness of interventions for prevention and treatment of these two conditions, especially when extrapolating short-term results from clinical trial follow-up.
Online supplementary material
Table S1. Follow-up information after index TIA or stroke
Table S2. 5-year hospital care resource use after index TIA or stroke
Table S3. 5-year present value hospital care costs after index TIA or stroke
Table S4. Predictors of 1- and 5-year hospital care costs after stroke
Acknowledgements
We are grateful to all patients who took part in the study. We thank all primary care practices and physicians who collaborate with OXVASC. We thank two anonymous referees for their valuable comments.
Sources of funding
RL-F is funded from an Economic and Social Research Council/Medical Research Council/National Institute for Health Research (NIHR) early career fellowship in economics of health. AMG is a NIHR senior investigator. PMR is a NIHR senior investigator and a Wellcome Trust senior investigator. OXVASC is funded by the UK Medical Research Council, the Dunhill Medical Trust, the Stroke Association, and the NIHR Biomedical Research Centre, Oxford. HERC obtains part of its funding from the NIHR.
Footnotes
Disclosures: RL-F is funded from an Economic and Social Research Council/Medical Research Council/National Institute for Health Research (NIHR) early career fellowship in economics of health.
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