One of the most difficult tasks in differential diagnosis of patients with septic syndrome at the Intensive Care Units is to differentiate between infection and non-infection etiology of this syndrome. In the last years, new parameters have played an important role in this area - C-reactive protein, Interleukin-6 and procalcitonin. The aim of the investigation was to compare these three parameters in differential diagnosis of the septic syndrome. The Cohort and Methods. The authors examined 56 patients (17 women and 39 men, mean age being 43 and 51 years, respectively) hospitalized at the Intensive Care Units who corresponded to the criteria of the syndrome of inflammatory response, sepsis or septic shock. A total of 99 examinations were done. The samples were taken up to 24 hours after the beginning of clinical symptomatology and submitted to the laboratory within four hours. Immediately afterwards the determination of concentrations of all three parameters - C-reactive protein, interlaukin-6 and procalcitonin, were done. The results of the examinations were compared to each other as well as to the diagnosis of sepsis – the confirmed infection etiology. Results: in all the evaluated parameters the authors detected significant differences between the values of entry examination and all measurements between the patients with the syndrome of systemic inflammatory response and septic shock as well as among patients with sepsis and the septic shock. Likewise, the authors confirmed significant differences between concentrations of all three parameters in comparing the patients with sepsis and those with the septic shock. Only in the case of procalcitonin there was a significant difference in concentration between patients with the syndrome of systemic inflammatory response of non-infectious etiology and those with sepsis. The concentration of procalcitonin was the only predictive marker of diagnosis with the correlation coefficient r = 0.7263, r2 = 0.5275, P < 0.00005. Conclusion: calcitonin proved to be the most specific parameter in demonstrating infection etiology in patients with the septic syndrome, its predictive value being higher than that of C-reactive protein and Interleukin- 6. Monitoring of calcitonin dynamism provides important information on efficiency of the applied antibiotic treatment. In patients with diagnostic uncertainties as far as the etiology of the septic syndrome is concerned; procalcitonin is the parameter of choice, while it may be supplemented with the examination of C-reactive protein.

        Key words: The syndrome of inflammatory response - sepsis - differential diagnosis - procalcitonin - Interleukin-6 - C-reactive protein