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Rheumatology Advance Access published online on July 17, 2008
Rheumatology, doi:10.1093/rheumatology/ken287
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Costs and quality of life of patients with ankylosing spondylitis in Hong Kong

T. Y. Zhu1, L.-S. Tam1, V. W.-Y. Lee2, W. W. Hwang1, T. K. Li1, K. K. Lee2 and E. K. Li1

1Department of Medicine and Therapeutics, Prince of Wales Hospital and 2School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China.

Correspondence to: T. Y. Zhu, Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China. E-mail: tracyzhu{at}cuhk.edu.hk


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Supplementary data
 Acknowledgements
 References
 
Objectives. To assess the annual direct, indirect and total societal costs, quality of life (QoL) of AS in a Chinese population in Hong Kong and determine the cost determinants.

Methods. A retrospective, non-randomized, cross-sectional study was performed in a cohort of 145 patients with AS in Hong Kong. Participants completed questionnaires on sociodemographics, work status and out-of-pocket expenses. Health resources consumption was recorded by chart review. Functional impairment and disease activity were measured using the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), respectively. Patients’ QoL was assessed using the Short Form-36 (SF-36).

Results. The mean age of the patients was 40 yrs with mean disease duration of 10 yrs. The mean BASDAI score was 4.7 and BASFI score was 3.3. Annual total costs averaged USD 9120. Direct costs accounted for 38% of the total costs while indirect costs accounted for 62%. Costs of technical examinations represented the largest proportion of total cost. Patients with AS reported significantly impaired QoL. Functional impairment became the major cost driver of direct costs and total costs.

Conclusion. There is a substantial societal cost related to the treatment of AS in Hong Kong. Functional impairment is the most important cost driver. Treatments that reduce functional impairment may be effective to decrease the costs of AS and improve the patient's QoL, and ease the pressure on the healthcare system.

KEY WORDS: Ankylosing spondylitis, Cost of illness, Quality of life


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Supplementary data
 Acknowledgements
 References
 
AS is a chronic inflammatory rheumatic disorder with a predilection for the axial skeleton. Its main clinical features are back pain and peripheral joint involvement. Patients may also show effects on extra-articular organs such as the eyes, heart and lungs [1–3]. The prevalence of AS in Chinese is about 0.2–0.3% [4, 5]. The disease is diagnosed in early adulthood and functional limitations may lead to work capacity impairment and increased healthcare resources consumption, as well as reduced quality of life (QoL) as a result of disability and pain [6–12]. Previous studies have shown that the economic impacts of AS on the society or patients were substantial and the costs are driven by the costs of losses of work capacity [6–8, 11]. However, very few studies incorporated patients’ QoL into the assessment and there is no such economic evaluation on the Chinese AS patients.

We construct this study to assess direct, indirect and total costs and identify cost drivers of patients with AS in a Chinese population in Hong Kong, encompassing costs no matter who accrues them, as well as to investigate the patients’ QoL using Short Form-36 (SF-36).


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Supplementary data
 Acknowledgements
 References
 
This was a non-randomized, cross-sectional, retrospective societal survey. A cohort of 145 patients was recruited during August 2005 to December 2006 from the rheumatology clinic at Prince of Wales Hospital. Eligible participants had to have a diagnosis of AS using the modified New York criteria [13] by rheumatologists or qualified medical practitioners, and to be Chinese and aged 18 yrs or older. Patients who were not capable to respond to a questionnaire (e.g. presence of dementia) were excluded. The Ethics Committee of the Chinese University of Hong Kong approved this study, and all patients provided written informed consent.

Costs matrix and healthcare system
Costs were determined from the societal perspective, which means that all costs were relevant. Direct costs represented all the health resources utilization delivered to the patients because of AS in the previous 12 months. Direct healthcare resources comprised (i) visits to healthcare providers; (ii) technical examinations (blood and imaging tests); (iii) hospital care (emergency visits and hospitalization); (iv) all drugs taken; (v) patients’ out-of-pocket expenses for health products, non-traditional therapies (e.g. hydrotherapy, acupuncture, massage), aid devices, traditional Chinese medication and other self purchases. Direct non-healthcare resources comprised (i) transportation fees; (ii) other expenses including paid helper from social worker, adaptation to houses and private household helper.

Indirect costs referred to the loss of productivity because of annual sick leave due to AS, work disability due to AS and days off from household work due to AS. A question ‘would you be employed if you were free from AS’ was used to differentiate whether the work disability was AS-related.

Hong Kong has a dual healthcare system where public and private sectors coexist [14]. Public healthcare is heavily subsidized, where patients pay a nominal charge for a physician consultation or hospitalization (including all the drugs and technical examinations), while charges of private healthcare vary greatly between hospitals. Because most of the patients will have some public/private healthcare utilization, we recorded them by different methods. Patient self-reported fees were recorded when a private facility was utilized. Public health services consumption was derived by medical records review.

Data collection
Participants had to complete a specially designed questionnaire comprising (i) sociodemographics; (ii) AS-specific function measured by the Bath Ankylosing Spondylitis Functional Index (BASFI) [15], disease activity measured by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) [16] and the SF-36, a validated generic instrument assessing QoL [17, 18]; (iii) an economic section on patients’ own investment in the previous year.

Patients’ medical records were then reviewed to elicit all the public healthcare resources utilization, including physician visits, technical examinations, prescribed drugs and hospital care in the previous year. Patients’ clinical features, such as disease duration and comorbid medical conditions were assessed by rheumatologists.

Costs calculation
For the public health resources, average per diem cost estimated by the Hospital Authority (S.S. No. 4 to Gazette D4633) was used (See Supplementary Table 1, available as supplementary data at Rheumatology online). Private health resources were reported by patients. The human capital approach was used to calculate indirect costs [19]. Wages were derived from Wage and Payroll Statistics, Census and Statistic Department of Hong Kong.

Statistical analysis
Stepwise multiple linear regression analysis was used to determine the drivers of the costs and the correlation between BASDAI/BASFI and SF-36 subscales. Log10 transformation of costs was performed to fit the normative assumptions. The cost drivers tested were patients’ age, sex, education level, duration of AS, BASDAI and BASFI scores. Two-sample t-test was used to test the difference of the SF-36 subscales between the sample and the general population. Data analysis was performed using the SPSS (version 13.0).


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Supplementary data
 Acknowledgements
 References
 
A total of 145 patients completed the questionnaires. Of them, 79% were males with a mean age of 40 yrs (S.D. 11.1) and mean disease duration of 10 yrs (S.D. 7.9). The mean BASDAI score was 4.7 (S.D. 2.1, median 4.6) and the mean BASFI score was 3.3 (S.D. 2.5, median 2.8). BASDAI and BASFI scores were strongly correlated (r = 0.73; P < 0.001).

Costs
No participants had ever used biologic drugs (e.g. infliximab or etanercept) during the study period. Total average annual costs were USD 9120 with a median of USD 4205 (range 136–64 901). Indirect costs accounted for a larger percentage (62%) of total costs (Table 1). Costs of technical examination accounted for the largest percentage (32%) of annual direct costs, followed by the costs of physician visit (22%). Although hospitalization was occasionally seen (reported by eight patients), it cost USD 687 per patient-year. Fifty-nine per cent of the patients reported out-of-pocket expenses due to AS, mainly on health product and non-traditional therapy. Very few patients reported private healthcare utilization (seven patients). Drug costs were low in the cohort, only 4% of annual direct costs.


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  		TABLE 1. Annual costs of AS patients (expressed in 2006 USD, 1 USD = 5.527 HKDa) (n = 145)

 
A large proportion of the sample reported productivity loss. Sixty-seven per cent of the patients were employed or self-employed. Thirty percent of the male and 43% of the female AS patients were unemployed (AS-related or not) in the cohort, which was about 3–7 times higher compared with the general Hong Kong population (unemployment rate 7.8% for males and 5.6% for females). Seventeen per cent of the patients reported work disability due to AS, among which 11% were unemployed and 6% had premature retirement because of AS. For those who were employed, 86% patients had taken sick leave during the past year, with a mean duration of 8 days.

Quality of life
All eight SF-36 scores of the sample were lower than that of the Hong Kong general population [20], with P-values of all comparisons <0.001 (Fig. 1). Results were consistent when the sample was separated by gender.


Figure 1
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  		FIG. 1. Mean (S.D.) SF-36 scores in AS and the Hong Kong general population [20]. PF, physical function; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social function; RE, role-emotional; MH, mental health; P < 0.001 in all the eight SF-36 subscales in AS compared with the general population in Hong Kong.

 
Multiple linear regressions were performed to explore the possible correlation between all the subscales of SF-36 and BADAI/BASFI scores. After adjustment by age and disease duration, significant correlation could be found between physical function and BASFI score (P = 0.002), social function and BASFI score (P = 0.013) and role-limitation due to emotion and BASDAI score (P = 0.043).

Cost determinants
Results of step-wise multiple linear regression analyses are showed in Table 2. BASDAI and BASFI influenced disease costs by different degrees. BASDAI was not correlated with costs, while functional impairment is clearly the strongest costs driver. BASFI predicted direct costs, indicating that patients with more functional impairment accrued more health resources consumption and costs. But as to indirect costs, none of the tested drivers can predict it. For total annual costs, only functional impairment played a role. Age, gender, education level, disease duration or disease activity were not costs drivers.


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  		TABLE 2. Results from multivariate linear regression analyses of cost drivers

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Supplementary data
 Acknowledgements
 References
 
To our knowledge, this is the first study aiming to investigate health resources utilization, direct medical costs, indirect costs and QoL of Chinese patients with AS in Hong Kong.

Mean direct costs per patient-year are 50% lower in Hong Kong than in Canada [11], but 49% higher than in USA [6]. However, comparisons of costs among different studies and across different diseases can be difficult, mainly due to differences in sampling, costs matrix used, data collection and international or regional variety of treatment practices.

In our sample, the general practice of management of AS in the public healthcare system requires routine follow-up (usually every 3–4 months but depending on the disease activity/severity). In order to monitor the disease progress and side-effects of drugs, each physician visit routinely requires series blood tests, such as complete blood count, liver and renal function, ESR and CRP. Sometimes image tests are required. This typical pattern of investigation may explain the high costs of technical examination. A large proportion of patients were using traditional medication, like NSAIDs or DMARDs, but the costs of these medications were 4% of the direct costs. The results were not consistent with the previous studies where hospital costs or medication costs were usually the largest components [6, 7, 11, 12]. This could be partly explained by the different healthcare system. In Hong Kong, most patients seek public healthcare resources, where resources are extremely limited. Chronic diseases, like AS, are mainly managed in the outpatient setting. Medication prescription is also restricted in the public healthcare system, where those new and high-cost drugs (such as the biologic agents) are not within the reimbursed system, and some traditional and less-expensive drugs are mostly used, incurring reasonably low medication costs.

Consistent with previous studies [6, 7, 11], indirect costs dominated total costs. Compared with UK [7] and Germany [12], annual indirect costs in our sample are lower. Employment rates may play a role. Seventy-two per cent of the patients in our cohort were employed, much higher than those in the UK study (51%) [7]. For those who were employed, productivity loss represented wages lost due to sick leave or lost time from work. For those who were unemployed or had early retirement, lost time from work would be much longer, resulting in a higher productivity loss. But in our sample, long-term sick leave is rare (only four patients reported annual sick leave >20 days). Thus, the results that indirect costs are lower may be partly explained by the higher employment rate in our sample. Even so, the unemployment rate of the cohort is still much higher than the general population in Hong Kong, reflecting that the working capacity of AS patients is seriously damaged.

A number of studies have found that disease severity is the major costs determinant, especially deteriorating physical function [6–8, 11, 12]; similar results were showed in our study. Functional impairment measured by BASFI was the most important costs driver of total costs and direct costs in our study. But one thing also showed was that BASDAI score was not a significant cost driver, which was not consistent with previous study. This may be explained by the relatively small sample size in our study. But because BASDAI and BASFI are highly correlated [21], we should still take BASDAI into account when using results from clinical trials.

As expected, compared with the general population, patients with AS showed significantly impaired function on all scales of the SF-36, revealing the fact that the disease affected patients across all major dimensions of health, including physical function, mental health and social functioning. Our results are supported by other studies [10, 22]. Results of regression analyses showed that not all the subscales are correlated with BASDAI/BASFI, indicating that there were some dimensions less affected by disease activity or severity.

There are some limitations to this study. The retrospective design and recall bias may affect the accuracy of the data, particularly that the recall period is long (12 months). Also notable is the fact that the sample is recruited from a rheumatologist clinic and with a large proportion (97%) of patients being under the age of 65 yrs. There is no solid reference regarding the referral percentage or situation of AS in Hong Kong. Whether a clinic-based cohort is consistent with a community-based cohort is questioned. But compared with a previous societal survey of AS in Hong Kong (patients recruited from two AS associations), age, disease activity and functional impairment of our cohort are similar to it [21].

Not withstanding these limitations, it is still clear that there is a substantially high societal cost in treatments of AS in Hong Kong and QoL of patients with AS is severely impaired. Unlike the Western countries, where the third part payer plays an important role, most of the patients with chronic diseases will seek for the public healthcare that is highly subsidized; thus, the costs showed in our study may exactly reflect the substantial heavy burden that AS has caused to society as well as government. Functional impairment is the most important costs driver, which inspires us of the need to investigate whether the treatment which can delay the disease process or reduce functional disability is an effective way to lower or avoid the high disease costs and improve the patients’ QoL.

Formula


   Supplementary data
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary data
Acknowledgements
 References
 
Supplementary data are available at Rheumatology Online.


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  		TABLE 3. Unit price of the main public healthcare resources (expressed in 2006 USD, 1 USD = 7.76 HKDa)

 

   Acknowledgements
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary data
 Acknowledgements
References
 
The authors would like to acknowledge all the AS patients for their considerable time and effort contributed toward this project, as well as their research assistant Tseung Lorraine for her contributions in data collection and entry.

Disclosure statement: The authors have declared no conflicts of interest.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary data
 Acknowledgements
 References
 

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Submitted 21 February 2008; revised version accepted 20 June 2008.
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