title: The prevalence of axial spondyloarthritis in the UK: a cross-sectional cohort study.
abstract: BACKGROUND
  Accurate prevalence data are important when interpreting diagnostic tests and planning for the health needs of a population, yet no such data exist for axial spondyloarthritis (axSpA) in the UK. In this cross-sectional cohort study we aimed to estimate the prevalence of axSpA in a UK primary care population.
  
  
  METHODS
  A validated self-completed questionnaire was used to screen primary care patients with low back pain for inflammatory back pain (IBP). Patients with a verifiable pre-existing diagnosis of axSpA were included as positive cases. All other patients meeting the Assessment of SpondyloArthritis international Society (ASAS) IBP criteria were invited to undergo further assessment including MRI scanning, allowing classification according to the European Spondyloarthropathy Study Group (ESSG) and ASAS axSpA criteria, and the modified New York (mNY) criteria for ankylosing spondylitis (AS).
  
  
  RESULTS
  Of 978 questionnaires sent to potential participants 505 were returned (response rate 51.6 %). Six subjects had a prior diagnosis of axSpA, 4 of whom met mNY criteria. Thirty eight of 75 subjects meeting ASAS IBP criteria attended review (mean age 53.5 years, 37 % male). The number of subjects satisfying classification criteria was 23 for ESSG, 3 for ASAS (2 clinical, 1 radiological) and 1 for mNY criteria. This equates to a prevalence of 5.3 % (95 % CI 4.0, 6.8) using ESSG, 1.3 % (95 % CI 0.8, 2.3) using ASAS, 0.66 % (95 % CI 0.28, 1.3) using mNY criteria in chronic back pain patients, and 1.2 % (95 % CI 0.9, 1.4) using ESSG, 0.3 % (95 % CI 0.13, 0.48) using ASAS, 0.15 % (95 % CI 0.02, 0.27) using mNY criteria in the general adult primary care population.
  
  
  CONCLUSIONS
  These are the first prevalence estimates for axSpA in the UK, and will be of importance in planning for the future healthcare needs of this population.
  
  
  BACKGROUND
  Current Controlled Trials ISRCTN76873217.
authors.affiliation: Rheumatology Department, Norfolk and Norwich University Hospital, Colney Lane, Norwich, Norfolk, NR4 7UY, UK. louise.hamilton@nnuh.nhs.uk.
authors.forename: Louise
authors.initials: L
authors.lastname: Hamilton
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, UK. A.Macgregor@uea.ac.uk.
authors.forename: Alex
authors.initials: A
authors.lastname: Macgregor
authors.affiliation: Radiology Department, Norfolk and Norwich University Hospital, Norwich, UK. andoni.toms@nnuh.nhs.uk.
authors.forename: Andoni
authors.initials: A
authors.lastname: Toms
authors.affiliation: Humbleyard Surgery, Norwich, UK. victoria.warmington@nhs.net.
authors.forename: Victoria
authors.initials: V
authors.lastname: Warmington
authors.affiliation: Humbleyard Surgery, Norwich, UK. edward.pinch@nhs.net.
authors.forename: Edward
authors.initials: E
authors.lastname: Pinch
authors.affiliation: Rheumatology Department, Norfolk and Norwich University Hospital, Colney Lane, Norwich, Norfolk, NR4 7UY, UK. karl.gaffney@nnuh.nhs.uk.
authors.forename: Karl
authors.initials: K
authors.lastname: Gaffney
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D013167:Spondylitis, Ankylosing / Q000175:diagnosis* / Q000453:epidemiology*; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult