A population-based assessment of systemic lupus erythematosus incidence and prevalenceresults and implications of using administrative data for epidemiological studies

Objectives. To estimate (i) systemic lupus erythematosus (SLE) incidence and prevalence using multiple sources of population-based administrative data; (ii) the sensitivity and specificity of case ascertainment methods; and (iii) variation in performance of each ascertainment approach, according to patient and physician characteristics. Methods. We examined the physician billing and hospitalization databases of the province of Quebec (1994-2003) covering all health care beneficiaries (similar to 7.5 million). We compared various approaches to ascertain SLE cases, using information from each database separately or combining sources; we then estimated the sensitivity and specificity of these alternative approaches. We used regression models to determine if sensitivity was independently influenced by patient or physician characteristics. Results. Using billing data, we calculated SLE incidence at 3.0/100 000 person-years [95% confidence interval (CI) 2.6-3.4]; prevalence was 32.8/100 000 persons, in 2003. Results were similar using hospitalization data. However, only a proportion of prevalent cases were identified as having SLE by both methods. Combining cases from billing and hospitalization data, we found a prevalence of 51/100 000 in 2003. Our latent class regression model estimated a prevalence of 44.7/100 000 (95% CI 37.4-54.7). We found high specificity for SLE diagnoses across all strategies and data sources; sensitivity ranged from 42.1 to 67.6, and was independently influenced by both patient and physician characteristics. Conclusions. In observational studies, particularly with administrative databases, SLE incidence and prevalence estimates differ considerably, according to the approach for case ascertainment. In the absence of gold standards, statistical modelling can provide sensitivity and specificity estimates for different approaches.