Systemic lupus erythematosus prevalence in the UK: methodological issues when using the General Practice Research Database to estimate frequency of chronic relapsing-remitting disease.

PURPOSE: The purpose of this study was to calculate the prevalence of systemic lupus erythematosus (SLE) between 1992 and 1998 using the General Practice Research Database (GPRD) METHODS: We identified all individuals who had contributed at least 3 years of data to the GPRD and who had a diagnosis of SLE with supporting evidence of their diagnosis. We calculated the annual age- and sex-specific prevalence of SLE. Additionally, we stratified the prevalence by years of data contributed to the GRPD.

RESULTS: In males the point estimate of the prevalence of SLE increased from 7.5/100,000 (CI(95) 6.3, 8.8) to 10.1/100,000 (CI(95) 7.8, 12.2) but this rise was not statistically significant. However, prevalence appeared to increase significantly amongst females from 42.6/100,000 (CI(95) 39.6, 45.6) in 1992 to 70.8/100,000 (CI(95) 65.1, 76.6) in 1998. This increase was mainly amongst women aged 50-79 and in those contributing more than 5 years of data and could not be explained by increasing incidence of SLE or decreasing mortality during the study period.

CONCLUSIONS: We found an increasing prevalence of SLE that could not be explained by increasing incidence or decreasing mortality. This is almost certainly an artefact caused by the increased likelihood of detecting or confirming cases of chronic relapsing-remitting diseases with increasing time contributed to the GPRD.