title: The ClASsification for Psoriatic ARthritis (CASPAR) criteria--a retrospective feasibility, sensitivity, and specificity study.
abstract: OBJECTIVE
  To evaluate the sensitivity, specificity, and feasibility of the ClASsification criteria for Psoriatic ARthritis (CASPAR) to retrospectively classify an existing research cohort.
  
  
  METHODS
  In total, 480 patient records were reviewed from the Royal National Hospital for Rheumatic Diseases Psoriatic Arthritis (PsA) cohort and for 100 consecutive controls with inflammatory arthritis from a general rheumatology clinic. The CASPAR score was modified for retrospective use; both "inflammation" and "current psoriasis" were recorded as present if they had ever been confirmed in the rheumatology clinic. Sensitivity and specificity of the CASPAR criteria were compared with expert clinical diagnosis.
  
  
  RESULTS
  A total of 480 database records were identified. Nine sets of records had been lost or destroyed. The diagnoses had changed in 15 cases, which were transferred to the control arm, leaving 456 patients with an expert diagnosis of PsA. Of 115 controls, 96 had rheumatoid arthritis, 5 osteoarthritis, 3 reactive arthritis, 3 seronegative arthritis, 3 undifferentiated arthralgia, 2 ankylosing spondylitis, 1 spondyloarthritis, and 2 systemic sclerosis. Sensitivity (99.7%) and specificity (99.1%) were both high and equivalent to previous reports. Sensitivity remained high even after inclusion of 7 PsA patients with insufficient data to complete the CASPAR assessment (sensitivity 98.2%, specificity 99.1%). The criteria were found to be easy and practical to apply to case records.
  
  
  CONCLUSIONS
  Our study demonstrates that the feasibility, specificity, and sensitivity of the CASPAR are maintained when adapted for retrospective use to classify an established research cohort.
authors.affiliation: Royal National Hospital for Rheumatic Diseases, Rheumatology, Upper Borough Walls, Bath BA11RL, UK. w.tillett@nhs.net
authors.forename: William
authors.initials: W
authors.lastname: Tillett
authors.forename: Luisa
authors.initials: L
authors.lastname: Costa
authors.forename: Deepak
authors.initials: D
authors.lastname: Jadon
authors.forename: Dinny
authors.initials: D
authors.lastname: Wallis
authors.forename: Charlotte
authors.initials: C
authors.lastname: Cavill
authors.forename: Jessica
authors.initials: J
authors.lastname: McHugh
authors.forename: Eleanor
authors.initials: E
authors.lastname: Korendowych
authors.forename: Neil
authors.initials: N
authors.lastname: McHugh
mesh_terms: D015535:Arthritis, Psoriatic / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology*; D015331:Cohort Studies; D016208:Databases, Factual; D006801:Humans; D012189:Retrospective Studies; D012680:Sensitivity and Specificity