Background: Sepsis is a life-threatening organ dysfunction that arises when a host responds insufficiently to an infection as bacteria enter the bloodstream. In recent years, SOFA scoring system has been used to identify poor organ functioning. Microbiological blood tests represent a gold standard in sepsis diagnostics. Reliable biomarkers for early detection of sepsis would greatly facilitate rapid and efficient treatment of sepsis. Methods: In a prospective non-interventional study we studied the diagnostic value of C-reactive protein (CRP), procalcitonin (PCT), neutrophil CD64 index, neutrophil granulocyte count and immature neutrophil count in patients with sepsis and patients with severe infection without sepsis. A total of 46 consecutive intensive-care-unit patients admitted for severe infection and 10 healthy controls were included. The patients were treated routinely according to the principles of good clinical practice. Results: Statistically significant differences between the two groups of patients have been established for the CD64 index, the PCT and the immature neutrophil count, whereas the differences in the CRP and the neutrophil granulocyte count are statistically non-significant. The highest diagnostic values were measured for the immature neutrophil count (AUC 0.91) and PCT (AUC 0.84). The combination of biomarkers has been shown to have same predictive values as the immature neutrophil count and the PCT.