Introduction: Determining which patients who meet systemic inflammatory response syndrome (SIRS) criteria have bacterial sepsis is a difficult challenge for emergency physicians. We sought to determine whether the neutrophil-to-lymphocyte ratio (NLR) could be used to exclude bacterial sepsis in adult patients who meet ≥2 SIRS criteria and are being evaluated for sepsis.

Methods: Consenting adult patients meeting ≥2 SIRS criteria and undergoing evaluation for sepsis were enrolled. We recorded patient age, gender, vital signs, and laboratory results. We then later reviewed health records for culture results, end organ dysfunction, survival to discharge, and final diagnoses.
Patients were classified as having sepsis if they met ≥2 SIRS criteria and were ultimately diagnosed with a bacterial source. We analyzed data using descriptive statistics and sensitivity and specificity analyses. A receiver operating characteristic curve (ROC) was created to determine test characteristics.

Results: A total of 231 patients had complete datasets. Patients’ median age was 69 (interquartile range [IQR] 54–81), and 49.6% were male. There were 154 patients (66.7%) ultimately diagnosed with sepsis with an identified bacterial source, while 77 patients with ≥2 SIRS criteria had non-infectious reasons for their presentations (33.3%). Septic patients had a median NLR 12.36 (IQR [interquartile range] 7.29–21.69), compared to those without sepsis (median NLR 5.62, IQR 3.89–9.11, P < 0.001). The NLR value of 3 applied as a cutoff for sepsis had a sensitivity of 96.8 (95% confidence interval [CI] 92.2–98.8), and a specificity of 18.2 (95% CI 10.6–29.0). The ROC for NLR had an area under the curve of 0.74.

Conclusion: The neutrophil-to-lymphocyte ratio is a sensitive tool to help determine which patients with abnormal SIRS screens have bacterial sepsis.