title: A validation study of a new classification algorithm to identify rheumatoid arthritis using administrative health databases: case-control and cohort diagnostic accuracy studies. Results from the RECord linkage On Rheumatic Diseases study of the Italian Society for Rheumatology.
abstract: OBJECTIVE
  To develop and validate a new algorithm to identify patients with rheumatoid arthritis (RA) and estimate disease prevalence using administrative health databases (AHDs) of the Italian Lombardy region.
  
  
  METHODS
  Case-control and cohort diagnostic accuracy study.
  
  
  METHODS
  In a randomly selected sample of 827 patients drawn from a tertiary rheumatology centre (training set), clinically validated diagnoses were linked to administrative data including diagnostic codes and drug prescriptions. An algorithm in steps of decreasing specificity was developed and its accuracy assessed calculating sensitivity/specificity, positive predictive value (PPV)/negative predictive value, with corresponding CIs. The algorithm was applied to two validating sets: 106 patients from a secondary rheumatology centre and 6087 participants from the primary care. Alternative algorithms were developed to increase PPV at population level. Crude and adjusted prevalence estimates taking into account algorithm misclassification rates were obtained for the Lombardy region.
  
  
  RESULTS
  The algorithms included: RA certification by a rheumatologist, certification for other autoimmune diseases by specialists, RA code in the hospital discharge form, prescription of disease-modifying antirheumatic drugs and oral glucocorticoids. In the training set, a four-step algorithm identified clinically diagnosed RA cases with a sensitivity of 96.3 (95% CI 93.6 to 98.2) and a specificity of 90.3 (87.4 to 92.7). Both external validations showed highly consistent results. More specific algorithms achieved >80% PPV at the population level. The crude RA prevalence in Lombardy was 0.52%, and estimates adjusted for misclassification ranged from 0.31% (95% CI 0.14% to 0.42%) to 0.37% (0.25% to 0.47%).
  
  
  CONCLUSIONS
  AHDs are valuable tools for the identification of RA cases at the population level, and allow estimation of disease prevalence and to select retrospective cohorts.
authors: Epidemiology Unit, Italian Society for Rheumatology, Milan, Italy.
authors: Greta
authors: G
authors: Carrara
authors: Epidemiology Unit, Italian Society for Rheumatology, Milan, Italy.
authors: Carlo A
authors: CA
authors: Scirè
authors: Department of Statistics and Quantitative Methods, Section of Biostatistics, Epidemiology and Public Health, University of Milano-Bicocca, Milan, Italy.
authors: Antonella
authors: A
authors: Zambon
authors: Research Laboratory and Academic Division of Clinical Rheumatology, Department of Internal Medicine, University of Genova, Genoa, Italy.
authors: Marco A
authors: MA
authors: Cimmino
authors: Information System and Management Control, Local Health Authority (ASL), Pavia, Italy.
authors: Carlo
authors: C
authors: Cerra
authors: Department of Medicine, Istituto Clinico Beato Matteo, Vigevano, Italy.
authors: Marta
authors: M
authors: Caprioli
authors: Department of Rheumatology, IRCCS San Matteo Foundation, Pavia, Italy.
authors: Giovanni
authors: G
authors: Cagnotto
authors: Department of Statistics and Quantitative Methods, Section of Biostatistics, Epidemiology and Public Health, University of Milano-Bicocca, Milan, Italy.
authors: Federica
authors: F
authors: Nicotra
authors: Department of Statistics and Quantitative Methods, Section of Biostatistics, Epidemiology and Public Health, University of Milano-Bicocca, Milan, Italy.
authors: Andrea
authors: A
authors: Arfè
authors: Information System and Management Control, Local Health Authority (ASL), Pavia, Italy.
authors: Simona
authors: S
authors: Migliazza
authors: Department of Statistics and Quantitative Methods, Section of Biostatistics, Epidemiology and Public Health, University of Milano-Bicocca, Milan, Italy.
authors: Giovanni
authors: G
authors: Corrao
authors: Division of Rheumatology, San Camillo Hospital, Rome, Italy.
authors: Giovanni
authors: G
authors: Minisola
authors: Department of Rheumatology, IRCCS San Matteo Foundation, Pavia, Italy.
authors: Carlomaurizio
authors: C
authors: Montecucco
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000453:epidemiology; D016022:Case-Control Studies; D015331:Cohort Studies; D016208:Databases, Factual / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008498:Medical Record Linkage; D016347:Medical Records Systems, Computerized / Q000706:statistics & numerical data*; D008875:Middle Aged; D015995:Prevalence; D012219:Rheumatology / Q000706:statistics & numerical data; D012680:Sensitivity and Specificity
keywords: EPIDEMIOLOGY; PUBLIC HEALTH
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