Prevalence of rheumatoid arthritis in Germany based on health insurance data. Regional differences and first results of the PROCLAIR study

Rheumatoid arthritis (RA) is the most common chronic inflammatory joint disease with a prevalence of up to 1 % in the adult population. This study describes the prevalence of RA diagnoses in outpatient health insurance claims data, based on different case definitions and stratified by age, sex and region of residence. Based on data from a nationwide statutory health insurance fund (BARMER GEK) from the year 2013, a cross-sectional study of insurants aged 18 years or older was conducted. The following case definitions were applied: A) a diagnosis of seropositive rheumatoid arthritis (M05) or other rheumatoid arthritis (M06) according to the international classification of diseases 10 German modification (ICD-10-GM) in at least two quarterly periods of the year 2013, B) case definition A plus determination of CaEuroreactive protein (CRP) or erythrocyte sedimentation rate (ESR) at least once, C) case definition B plus specific drug therapy and D) case definition A plus treatment by a rheumatologist. Raw as well as age and sex-standardized prevalences were calculated and stratified according to the federal state. The study population consisted of 7,155,315 insurants of whom 60.2 % were female. Overall, RA prevalences for the respective case definitions were 1.62 % (A), 1.11 % (B), 0.94 % (C) and 0.64 % (D). When standardized to the German population the prevalences were 1.38 % (A), 0.95 % (B), 0.81 % (C) and 0.55 % (D). The proportion of women was approximately 80 % for all case definitions. Prevalences increased with age, peaking in the age group 70-79 years old and showing the highest values in eastern and the lowest in southern Germany for raw as well as standardized measures. Regional differences in the prevalence of RA diagnoses in health insurance claims data were observed independent of age, sex and case definition. The expected prevalence according to the results of international studies was best achieved when case definitions with CRP or ESR were considered.