We have estimated the annual costs incurred by persons with SLE in a large US cohort, including the direct costs associated with the provision of health care and the costs associated with changes in work productivity. This analysis indicates that persons with SLE incur a mean annual direct cost of $12,643 in 2004 US dollars. Participants of working age incurred mean annual productivity costs of $8,659, assuming an average national hourly wage of $18.09. Our regression analyses showed that the strongest predictors of increased direct costs were greater disease activity, longer disease duration, and worse mental and physical health status (as assessed by the SF-12 health status questionnaire), whereas older age predicted lower direct costs. Older age has been shown to be a predictor for decreased costs in one other study of SLE patients (15
), whereas disease activity and worse physical health status have been shown to predict higher costs (14
). With respect to productivity costs, older age, greater disease activity, and worse physical and mental health status predicted higher costs. These predictors are similar to those seen in previous studies, which also showed disease activity and physical health status to be significant predictors of productivity costs (14
The published literature contains few studies of costs in SLE. Although differences in methodologies make comparisons difficult, a discussion of some of these studies will help put our results in perspective. One of the most comprehensive is the Tri-National Study by Clarke et al, in which health resource use was compared among SLE patients attending tertiary care clinics in 3 different countries: the US, Canada, and the UK (11
). In order to facilitate comparisons among patients from the 3 countries, this analysis valued resources using only Canadian prices. Mean cumulative direct costs per patient over 4 years in the US, Canada, and the UK were $20,244, $15,845, and $17,647, respectively (2002 Canadian dollars). Therefore, annual direct costs in the US were estimated at approximately $5,061 (2002 Canadian dollars) or $3,347 (2004 US dollars). Our study used American prices, which are often much higher than prices in other countries (28
), and has likely resulted in more accurate costs for persons with SLE living in the US. In the only other study assessing health resource use in SLE patients from the US, Nichol and colleagues assessed the association between ethnicity, resource use, and direct medical costs in a population-based study of California Medicaid patients with SLE (29
). This study demonstrated that all ethnic groups incurred similar monthly costs at study entry (approximately $900 in 2002 US dollars); however, over 3 years, Hispanics had increasingly lower monthly costs (approximately $200 at 3 years), whereas the costs incurred by whites and African Americans remained similar to the baseline level.
Health care costs of several rheumatic diseases were compared in a study by Huscher et al using a German national database (14
). This study showed that patients with SLE incurred mean annual direct costs of €3,191, whereas patients with RA incurred costs of €4,737, patients with ankylosing spondylitis €3,676, and patients with psoriatic arthritis €3,156. Direct costs were considerably lower in patients with SLE than in patients with RA; however, this difference was due in large part to differences in the cost of medications. Patients with RA incurred mean total medication costs of €1,843, representing 38.9% of total direct costs, whereas patients with SLE incurred mean total medication costs of €850, representing 26.6% of total direct costs. Although there were important differences in the methodologies used and the health care systems studied, medication costs represented a very similar percentage of total direct costs in our study (25.7%). However, as seen in RA, the proportion of direct costs attributable to medications will likely increase in the future, because newer and more expensive therapies are introduced in the treatment of SLE (7
A comparison of our estimated health care costs with national average per capita expenditures for a similar array of services highlights the high costs incurred in the care of persons with SLE. In 2004, the average per capita expenditure in the US for hospital and nursing home care, physician and clinical services, other professional services, and prescription drugs was $4,482 (30
). In our study, persons with SLE incurred approximately 3-fold greater direct health care costs than the national per capita average. Participants with the lowest level of disease activity incurred almost twice this national average, whereas those with the highest level of disease activity incurred 4 times the national average per capita cost.
A number of published studies have evaluated work productivity among persons with SLE, while only 2 have calculated productivity costs. Again, methodologies among studies differ considerably and comparisons should be made with caution. In a followup to the Tri-Nation Study by Clarke et al described above, productivity costs over a 4-year period were calculated for patients with SLE from the US, Canada, and the UK. To facilitate comparisons, Canadian age- and sex-matched average wages were used to estimate costs for subjects from all 3 countries (12
). Over 4 years, cumulative costs due to diminished productivity in paid labor in the US, Canada, and the UK were $56,745, $38,642, and $42,213 (2002 Canadian dollars), respectively. Therefore, annual productivity cost in the US was estimated at approximately $14,186 (2002 Canadian dollars) or $9,384 (2004 US dollars). In that study, participants were queried about the number of hours they missed from their current work schedule and the number of additional hours they would work if not ill. In contrast, our study, which showed mean productivity costs of $8,659, assessed the difference between the actual number of hours participants reported working in the year their SLE was diagnosed and the number of hours they currently work. Our methods allowed us to capture both decreases and increases in productivity, which may explain the somewhat lower productivity costs in our study. In fact, for certain participants with low levels of disease activity, work productivity actually increased since SLE diagnosis. The study by Huscher et al, making assessments based on sick leave and permanent work disability, estimated even higher productivity costs (14
). Patients with SLE incurred mean annual productivity costs of €11,220, which converts to approximately $10,485 (2004 US dollars).
A number of studies have assessed work disability in SLE without calculating associated productivity costs (31
). Two German studies assessed employment rates of individuals with SLE and compared them with other rheumatic conditions and with the general population. After appropriate matching, an equal proportion of SLE and RA patients (46%) remained employed (32
). Standardized employment ratios (SERs; ratio of observed to expected number of patients employed) were used to compare employment rates between individuals with SLE and a matched normal population. For individuals with a disease duration less than 6 years, employment rates did not differ from the general population; however, with greater disease duration, fewer individuals with SLE were working (SER 0.8 at 6–10 years and SER 0.68 at >10 years). Yelin et al, using data from the LOS cohort used in the present study, showed that employment declined from 74% at the time of SLE diagnosis to 48% at the time of the study (2004) (16
). Among participants working at diagnosis, the proportion employed declined by 15%, 36%, and 63% after 5, 10, and 20 years, respectively.
As with all studies that rely on patient-reported data, recall bias may be a potential limitation of our study, which required participants to recall use and employment over a 1-year period. Although there is little information regarding the ideal frequency and recall period for patient-reported economic questionnaires, a shorter recall period may have been preferred. For example, in one study, patient-reported questionnaires administered every 3 months yielded results similar to payer data (33
). Furthermore, we were not able to separate costs that were related to SLE from those that were not. As such, all health care costs were considered in our estimations of direct costs, and not only the additional costs incurred as a result of SLE. Although we attempted to assess costs from a societal perspective, which include all costs regardless of payer, we were not able to evaluate all cost components. Certain direct costs, such as those incurred for transportation and for diagnostic tests obtained in the outpatient setting, were not included. Our analysis of productivity costs did not capture diminished productivity in nonpaid work such as housework and childrearing, which may be particularly relevant in diseases that affect a predominantly female population (10
). Furthermore, our study design did not allow us to provide estimates of productivity costs using the friction method, which assumes that the economic cost to society is limited to the period required to replace the disabled employee, and typically generates lower estimates. Finally, although participants of this study reside in 41 different states, the majority (72%) resides in California, and so inference beyond California is limited.
In summary, SLE imposes a considerable financial burden, not only because of the health care resources that are consumed in the management of this complex disease, but also because of the loss of productivity due to work disability. The hope is that efforts to improve the care and treatment of persons with SLE will improve outcomes and help offset these considerable personal and societal costs.