Calprotectin as a Diagnostic Marker for Lower Respiratory Tract Infection and Sepsis in the Emergency Department.

Background: Calprotectin, a neutrophil activation marker, is a promising diagnostic biomarker for infection and sepsis, but its usefulness in the emergency department (ED) is unclear. The aim of this study was to investigate the diagnostic value of calprotectin for sepsis and the source of infection in the ED. Methods: A total of 583 prospectively included patients presenting with suspected sepsis to the ED of a university hospital in southern Sweden were analyzed. Calprotectin was measured in plasma samples obtained at admission. Results: Mean age was 69 years and 49% were female. Calprotectin discriminated between sepsis and noninfectious systemic inflammatory response syndrome with an area under the curve (AUC) of 0.63, but was not an independent predictor in multivariable analysis including C-reactive protein (CRP). The Modified Early Warning Score did not show any discriminatory ability. Calprotectin and CRP discriminated between lower respiratory tract infection and (1) upper respiratory tract infection, (2) urinary tract infection, and (3) other sources of infection. Addition of calprotectin to CRP significantly increased the AUC for lower versus upper respiratory tract infection and lower respiratory tract infection versus urinary tract infection. Calprotectin was an independent predictor for all outcomes while CRP was only an independent predictor of lower versus upper respiratory tract infection. Conclusions: Calprotectin may improve differentiation of lower respiratory tract infections from upper respiratory tract infections and urinary tract infections in patients presenting to the ED with sepsis. Further research is needed to clarify if calprotectin adds diagnostic value to standard clinical assessment.