title: Validity of gout diagnosis in Swedish primary and secondary care - a validation study.
abstract: BACKGROUND
  The diagnostic golden standard for gout is to detect monosodium urate (MSU) crystals in synovial fluid. While some gout classification criteria include this variable, most gout diagnoses are based on clinical features. This discrepancy between clinical practice and classification criteria can hinder gout epidemiological studies. Here, the objective was to validate gout diagnoses (International Classification of Diseases (ICD)-10 gout codes) in primary and secondary care relative to five classification criteria (Rome, New York, ARA, Mexico, and Netherlands). The frequency with which MSU crystal identification was used to establish gout diagnosis was also determined.
  
  
  METHODS
  In total, 394 patients with ≥1 ICD-10 gout diagnosis between 2009 and 2013 were identified from the medical records of two primary care centers (n = 262) and one secondary care center (n = 132) in Gothenburg, Sweden. Medical records were assessed for all classification criteria.
  
  
  RESULTS
  Primary care patients met criteria cutoffs more frequently when ≥2 gout diagnoses were made. Even then, few primary care patients met the Rome and New York cutoffs (19 % and 8 %, respectively). The ARA, Mexico, and Netherlands cutoffs were met more frequently by primary care patients with ≥2 gout diagnoses (54 %, 81 %, and 80 %, respectively). Mexico and Netherlands cutoffs were met more frequently by the rheumatology department patients (80 % and 71 %, respectively), even when patients with only 1 gout diagnosis were included. Analysis of MSU crystals served to establish gout diagnoses in only 27 % of rheumatology department and 2 % of primary care cases.
  
  
  CONCLUSIONS
  If a patient was deemed to have gout at ≥2 primary care center or ≥1 rheumatology-center visits according to an ICD-10 gout code, the positive predictive value of this variable in relation with the Mexico and Netherlands classification criteria was ≥80 % for both primary care and rheumatology care settings in Sweden. MSU crystal identification was rarely used to establish gout diagnosis.
authors.affiliation: Department of Rheumatology and Inflammation Research, Institute of Medicine, Sahlgrenska Academy at the University of Gothenburg, P.O. Box 480, 405 30, Gothenburg, Sweden. mats.dehlin@vgregion.se.
authors.forename: Mats
authors.initials: M
authors.lastname: Dehlin
authors.affiliation: Department of Rheumatology and Inflammation Research, Institute of Medicine, Sahlgrenska Academy at the University of Gothenburg, P.O. Box 480, 405 30, Gothenburg, Sweden. kalliopi.stasinopoulou@vgregion.se.
authors.forename: Kalliopi
authors.initials: K
authors.lastname: Stasinopoulou
authors.affiliation: Department of Rheumatology and Inflammation Research, Institute of Medicine, Sahlgrenska Academy at the University of Gothenburg, P.O. Box 480, 405 30, Gothenburg, Sweden. lennart.jacobsson@gu.se.
authors.forename: Lennart
authors.initials: L
authors.lastname: Jacobsson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000032:analysis; D003460:Crystallization; D005260:Female; D006073:Gout / Q000175:diagnosis* / Q000453:epidemiology / Q000378:metabolism; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D011237:Predictive Value of Tests; D011320:Primary Health Care; D015203:Reproducibility of Results; D063127:Secondary Health Care; D013548:Sweden / Q000453:epidemiology; D013582:Synovial Fluid / Q000737:chemistry*; D014527:Uric Acid / Q000032:analysis
chemical_list: D015415:Biomarkers; D014527:Uric Acid