title: Enriched administrative data can be used to retrospectively identify all known cases of primary subarachnoid hemorrhage.
abstract: OBJECTIVE
  We derived and validated a method to screen all hospital admissions for 1° subarachnoid hemorrhage (SAH) by retrospectively implementing recognized diagnostic criteria.
  
  
  METHODS
  A screen for 1° SAH was developed using two previously created registries. Screen-positive cases underwent diagnosis confirmation with primary record review. A review of all patient hospital encounters with the diagnostic code for 1° SAH, and cross-referencing with an existing SAH registry was undertaken to identify missed cases.
  
  
  RESULTS
  Three subscreens were combined to form the 1° SAH screen (sensitivity: 98.4% [95% CI: 91.7-99.7%], specificity: 93.4% [95% CI: 90.4-95.4%], n = 455 patients in validation sample). From 1,699 screen-positive admissions between July 1, 2002 and June 30, 2011, we identified 831 true cases of SAH of which 632 patients had 1° SAH from ruptured aneurysm/arteriovenous malformation (sensitivity: 96.5% [95% CI: 94.8-97.8%], specificity: 40.3% [95% CI: 38.1-42.6%]). A review of all encounters with a diagnostic code for 1° SAH yielded additional 22 true cases.
  
  
  CONCLUSIONS
  When positive, our 1° SAH screen significantly increases the probability of this diagnosis in a particular hospitalization. The addition of patient hospitalizations encoded with the diagnostic code for 1° SAH improved sensitivity. Together, these methods represent the best way to retrospectively identify all cases of 1° SAH within an extensive sampling frame.
authors.affiliation: Department of Medicine (Critical Care), The Ottawa Hospital, Ottawa, Canada; Ottawa Hospital Research Institute, Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada. Electronic address: senglish@ohri.ca.
authors.forename: Shane W
authors.initials: SW
authors.lastname: English
authors.affiliation: Department of Medicine (Critical Care), The Ottawa Hospital, Ottawa, Canada; Ottawa Hospital Research Institute, Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada.
authors.forename: Lauralyn
authors.initials: L
authors.lastname: McIntyre
authors.affiliation: Ottawa Hospital Research Institute, Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada.
authors.forename: Dean
authors.initials: D
authors.lastname: Fergusson
authors.affiliation: Department of Anesthesia (Critical Care), Hôpital de L'Enfant-Jésus, Québec City, Canada.
authors.forename: Alexis
authors.initials: A
authors.lastname: Turgeon
authors.affiliation: Department of Medicine, The Ottawa Hospital, Ottawa, Canada.
authors.forename: Cathy
authors.initials: C
authors.lastname: Sun
authors.affiliation: Ottawa Hospital Research Institute, Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada; Department of Medical Imaging (Neuro-Interventional Section), The Ottawa Hospital, Ottawa, Canada.
authors.forename: Marlise P
authors.initials: MP
authors.lastname: dos Santos
authors.affiliation: Department of Medical Imaging (Neuro-Interventional Section), The Ottawa Hospital, Ottawa, Canada.
authors.forename: Cheemun
authors.initials: C
authors.lastname: Lum
authors.affiliation: Department of Surgery (Neuro-Surgery), The Ottawa Hospital, Ottawa, Canada.
authors.forename: John
authors.initials: J
authors.lastname: Sinclair
authors.affiliation: Department of Medicine, The Ottawa Hospital, Ottawa, Canada.
authors.forename: Alan
authors.initials: A
authors.lastname: Forster
authors.affiliation: Ottawa Hospital Research Institute, Clinical Epidemiology Program, University of Ottawa, Ottawa, Canada; Department of Medicine, The Ottawa Hospital, Ottawa, Canada.
authors.forename: Carl
authors.initials: C
authors.lastname: van Walraven
mesh_terms: D000465:Algorithms; D001344:Autopsy; D001663:Bilirubin / Q000134:cerebrospinal fluid; D015415:Biomarkers / Q000134:cerebrospinal fluid; D016208:Databases, Factual; D003952:Diagnostic Imaging; D006751:Hospital Information Systems; D006801:Humans; D008403:Mass Screening / Q000379:methods; D009864:Ontario / Q000453:epidemiology; D012042:Registries; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013345:Subarachnoid Hemorrhage / Q000453:epidemiology*
chemical_list: D015415:Biomarkers; D001663:Bilirubin
keywords: Administrative data; Cohort; Diagnostic criteria; Retrospective disease registry; Screen; Subarachnoid hemorrhage