title: An algorithm to identify rheumatoid arthritis in primary care: a Clinical Practice Research Datalink study.
abstract: OBJECTIVE
  Rheumatoid arthritis (RA) is a multisystem, inflammatory disorder associated with increased levels of morbidity and mortality. While much research into the condition is conducted in the secondary care setting, routinely collected primary care databases provide an important source of research data. This study aimed to update an algorithm to define RA that was previously developed and validated in the General Practice Research Database (GPRD).
  
  
  METHODS
  The original algorithm consisted of two criteria. Individuals meeting at least one were considered to have RA. Criterion 1: ≥ 1 RA Read code and a disease modifying antirheumatic drug (DMARD) without an alternative indication. Criterion 2: ≥ 2 RA Read codes, with at least one 'strong' code and no alternative diagnoses. Lists of codes for consultations and prescriptions were obtained from the authors of the original algorithm where these were available, or compiled based on the original description and clinical knowledge. 4161 people with a first Read code for RA between 1 January 2010 and 31 December 2012 were selected from the Clinical Practice Research Datalink (CPRD, successor to the GPRD), and the criteria applied.
  
  
  RESULTS
  Code lists were updated for the introduction of new Read codes and biological DMARDs. 3577/4161 (86%) of people met the updated algorithm for RA, compared to 61% in the original development study. 62.8% of people fulfilled both Criterion 1 and Criterion 2.
  
  
  CONCLUSIONS
  Those wishing to define RA in the CPRD, should consider using this updated algorithm, rather than a single RA code, if they wish to identify only those who are most likely to have RA.
authors.affiliation: Arthritis Research UK Primary Care Centre, Institute for Primary Care & Health Sciences, Keele University, Keele, UK.
authors.forename: Sara
authors.initials: S
authors.lastname: Muller
authors.affiliation: Arthritis Research UK Primary Care Centre, Institute for Primary Care & Health Sciences, Keele University, Keele, UK.
authors.forename: Samantha L
authors.initials: SL
authors.lastname: Hider
authors.affiliation: Centre for Translational Inflammation Research, School of Immunity and Infection, University of Birmingham, Birmingham, UK Department of Rheumatology, Sandwell and West Birmingham Hospitals NHS Trust, Birmingham, UK.
authors.forename: Karim
authors.initials: K
authors.lastname: Raza
authors.affiliation: Centre for Translational Inflammation Research, School of Immunity and Infection, University of Birmingham, Birmingham, UK.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Stack
authors.affiliation: Arthritis Research UK Primary Care Centre, Institute for Primary Care & Health Sciences, Keele University, Keele, UK.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Hayward
authors.affiliation: Arthritis Research UK Primary Care Centre, Institute for Primary Care & Health Sciences, Keele University, Keele, UK.
authors.forename: Christian D
authors.initials: CD
authors.lastname: Mallen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D018501:Antirheumatic Agents / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000188:drug therapy; D059019:Clinical Coding; D016208:Databases, Factual; D005260:Female; D058006:General Practice; D006801:Humans; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care; D055815:Young Adult
chemical_list: D018501:Antirheumatic Agents
keywords: EPIDEMIOLOGY; PRIMARY CARE; RHEUMATOLOGY