Red Flags For Necrotizing Fasciitis: A Case Control Study

• delayed diagnosis of necrotizing fasciitis (NF) is associated with worse outcomes
• this is the first study to directly assess diagnostic accuracy of the clinical examination for NF
• no individual findings on history or physical examination are sufficiently sensitive to rule out NF
• however, the absence of all 9 ‘red flags’ may rule out NF
• and presence of 3 or more ‘red flags’ may rule in NF
• if future prospective studies validate these findings, there will be a potential opportunity to expedite NF diagnosis and improve patient outcomes

Objectiveto examine the diagnostic accuracy of traditional ‘red flags’ for necrotizing fasciitis (NF) on history and physical examination.Methodsretrospective 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.ResultsThere 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).ConclusionsWhen 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.