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 is unclear. Aim The aim of this study was to investigate the diagnostic value of calprotectin for sepsis and the source of infection in the emergency department. Methods 583 prospectively included patients presenting with suspected sepsis to the emergency department of a university hospital in southern Sweden were analysed. Calprotectin was measured in plasma samples obtained at admission. Results Mean age was 69 years and 49 % were female. Calprotectin discriminated between sepsis and non-infectious systemic inflammatory response syndrome with an AUC of 0.63, but was not an independent predictor in multivariable analysis including C-reactive protein. The Modified Early Warning Score did not show any discriminatory ability. Calprotectin and CRP discriminated between lower respiratory tract infection and i) upper respiratory tract infection, ii) urinary tract infection and iii) other sources of infection. Addition of calprotectin to CRP significantly increased the AUC for lower vs upper respiratory tract infection and lower respiratory tract infection vs urinary tract infection. Calprotectin was an independent predictor for all outcomes while C-reactive protein was only an independent predictor of lower vs upper respiratory tract infection. Conclusion 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.