title: Red Flags for Necrotizing Fasciitis: A Case Control Study.
abstract: OBJECTIVE
  to examine the diagnostic accuracy of traditional 'red flags' for necrotizing fasciitis (NF) on history and physical examination.
  
  
  METHODS
  retrospective study of all cases of NF admitted to a large tertiary care hospital between January 1 2004 and December 31 2013, each matched to two control patients with cellulitis. We determined the diagnostic test characteristics of clinical features for distinguishing NF from cellulitis, with emphasis on positive (LR+) and negative (LR-) likelihood ratios.
  
  
  RESULTS
  There were no individual findings with sufficient sensitivity to rule out NF (sensitivity ≤ 85% and LR- ≥ 0.5 for all findings). The clinical features that most significantly increased the odds of NF were recent surgery (LR+ 7.0) pain-out-of-proportion (LR+ 4.5), diarrhea (LR+ 6.0), hypotension (LR+ 8.0), altered mental status (LR+ 3.3), erythema progressing beyond margins (LR+3.1), fluctuance (LR+ 5.0), hemorrhagic bullae (LR+ 8.0) and skin necrosis (LR+ 30.0). Each individual finding conferred low sensitivity, but absence of all nine ruled out NF (LR- 0.04). The presence of >=3 findings ruled in NF (LR+ undefined).
  
  
  CONCLUSIONS
  When considered together, the traditional 'red flags' for NF may be sufficient to rule in or rule out the diagnosis. If future prospective studies validate these findings, there will be a potential opportunity to expedite NF diagnosis and improve patient outcomes.
authors.affiliation: Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada. Electronic address: khalidmohammed.alayed@sunnybrook.ca.
authors.forename: Khalid Al
authors.initials: KA
authors.lastname: Alayed
authors.affiliation: Sunnybrook Research Institute, Toronto, Ontario, Canada. Electronic address: charlie.tan@medportal.ca.
authors.forename: Charlie
authors.initials: C
authors.lastname: Tan
authors.affiliation: Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada; Division of Infectious Diseases, Department of Medicine, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada. Electronic address: nick.daneman@sunnybrook.ca.
authors.forename: Nick
authors.initials: N
authors.lastname: Daneman
mesh_terms: D002481:Cellulitis / Q000175:diagnosis; D003937:Diagnosis, Differential; D019115:Fasciitis, Necrotizing / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies
keywords: case control study; cellulitis; diagnosis; diagnostic accuracy; necrotizing fasciitis