CRP and infection: In conclusion, according to the results of our study, including elderly critically ill patients, the diagnostic accuracy of PCT for sepsis and infected without sepsis is higher than that of CRP and WBC. We found that PCT is a more accurate marker for differentiating infected without sepsis and sepsis while CRP and WBC are not. More studies are needed to determine the PCT and CRP kinetics in elderly patients and identify the optimal cut-off point for PCT levels at different stages of infection.