A Simple Model to Help Distinguish Necrotizing Fasciitis from Nonnecrotizing Soft Tissue Infection

Background: Necrotizing fasciitis (NF) has been associated with certain "hard" clinical signs (hypotension, crepitance, skin necrosis, bullae, and gas on x-ray), but these may not always be present. Using results of a previous study, we developed a simple model to serve as an adjunctive tool in diagnosing NF (admission WBC > 15.4 x 10(9)/L or serum sodium [Na] < 135 mmol/L) and determined its ability to distinguish between patients with NF and nonnecrotizing soft tissue infection (non-NF).

Study Design: A retrospective review was conducted of consecutive NF (n=31) and non-NF patients (n= 328) treated at a single institution during an 11-month period. Comparison of admission vital signs, physical examination findings, radiology results, and number of patients meeting model criteria was performed.

Results: Ninety percent of NF patients and 24% of non-NF patients met model criteria (p < 0.0001). The model had a sensitivity of 90%, a specificity of 76%, a positive predictive value of 26%, and a negative predictive value of 99% for diagnosing NF. Nineteen (61%) NF patients had no "hard" signs of NF; the model correctly classified 18 (95%) of these patients.

Conclusions: Admission WBC greater than 15.4 x 10(9)/L and serum Na less than 135mmol/L are useful parameters that may help to distinguish NF from non-NF infection, particularly when classic "hard" signs of NF are absent.