C-reactive protein as an indicator of bacterial infection of adult patients in the emergency department

Abstract

Background: This investigation evaluates the feasibility of using C-reactive protein (CRP) levels as an indicator of bacterial infection of adult patients in the Emergency Department (ED), by comparing them with clinical signs and routine laboratory tests.

Methods: One hundred and fifty adult atraumatic patients admitted through the ED of Linkou Chang Gung Memorial Hospital were consecutively enrolled. Seventy-nine patients had documented infection, and 58 had no infection. Body temperature (BT), white blood cell (WBC) count, CRP levels, and the presence of systemic inflammatory response syndrome (SIRS) were compared between the infected and uninfected groups.

Results: SIRS was the most sensitive indicator of bacterial infection (sensitivity 84.8%), but it had a 37.9% false-positive rate. BT and WBC count were more specific (at 89.7% and 84.5%) but less sensitive (at 48.1% and 43.0%, respectively). Using Youden's Index, the best cut-off value for CRP was 60 mg/l (sensitivity 67.1%, specificity 94.8%, positive predictive value 94.6%, and negative predictive value 67.9%). The area under the receiver operating characteristics (ROC) curve was highest for CRP (at 0.88), followed by BT (at 0.77) and WBC (at 0.67) (all p < 0.05).

Conclusion: CRP is a better indicator of bacterial infection than either BT or WBC count for adult atraumatic ED patients. A low serum CRP level cannot safely be used to exclude the presence of infection.