Oral and Poster Presentation ARA-NSW 2021 - 43rd Annual NSW Branch Meeting

Estimating the true prevalence of rheumatoid arthritis in Australian women (#10)

Louise Koller-Smith 1 , Ahmed M Mehdi 1 , Lyn March 2 3 , Leigh Tooth 4 , Gita Mishra 4 , Ranjeny Thomas 1
  1. Diamantina Institute, University of Queensland, Wollongabba, Queensland, Australia
  2. Florance and Cope Professorial Department of Rheumatology, Royal North Shore Hospital, Sydney, New South Wales
  3. Institute of Bone and Joint Research, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales
  4. University of Queensland, School of Public Health, University of Queensland, Brisbane, Queensland

Introduction: Currently, all estimates of rheumatoid arthritis (RA) prevalence in Australia are through self-report. Overseas validation studies have found that self-report substantially overestimates true RA, but addition of self-reported medications to case-finding definitions improves validity. Best validated global estimates suggest a prevalence of RA of around 0.5% overall and around 0.7% in women. No studies have been done in an Australian context.

Aim: To compare self-reported RA with other case-finding definitions formulated using self-reported medications, longitudinal self-report, and administrative data

Methods: We used prospectively collected data from the Australian Longitudinal Study on Women’s Health (ALSWH), collected between 2005 and 2015. Data were linked to administrative data from the PBS/RPBS and hospital admissions. RA cases were selected from each of the data sources available. For medications, a ‘mid’ definition was devised that included patients reporting DMARDs and/or prednisone, while a ‘strict’ definition included patients reporting DMARDs only. Patients on anti-psoriatic medications were excluded. Longitudinal agreement between self-reported RA diagnosis in surveys 3 years apart ascertained consistency of self-report. The RA prevalence from each data source and the degree of overlap was compared.

Results: A total of 34 993 responses from participants aged 79-84 years, 59-64 years, 56-61 years and 37-42 years were identified from questions on self-reported RA and medications. Prevalence according to self-report was 5.4%, from self-reported medications 1.5-3.3%, and from a combination of self-reported diagnosis and medications was 0.9-1.3%. From administrative data sources, prevalence was 2.8% for PBS dispensed 'strict' medications and 1.1% amongst all admitted patients. A combination definition from administrative data gave a prevalence of 0.5%. Overlapping of cases according to different data sources was lower than expected. (This information will be provided in table and diagram form)

Conclusion: Establishing a case finding method for use in incidence and prevalence data and large population studies is complex, with no single definition expected to capture all cases. While self-reported RA includes both false positives and false negatives on its own, a combination of administrative data and self-reported RA appears to estimate RA prevalence with greater accuracy.