PATHFAST™ B・R・A・H・M・S PCT is an immunoassay for the in vitro quantitative determination of Procalcitonin (PCT) concentration in whole blood, plasma or serum. PCT is used as a marker of host response to bacterial infection. PATHFAST™ B・R・A・H・M・S PCT is used as an aid in the early detection and differential diagnosis of clinically relevant bacterial infections, in the assessment of the degree of septic severity and in the risk stratification of the outcome of patients with systemic bacterial infection, sepsis, severe sepsis and septic shock. PATHFAST™ B・R・A・H・M・S PCT is also used as an aid in decision making on antibiotic therapy for patients with lower respiratory tract infections (LRTI) and in decision making on antibiotic discontinuation for patients with suspected or confirmed sepsis. PCT is used as an aid in the diagnosis of sepsis, severe sepsis and septic shock in systemic inflammatory response of bacterial infection as well as in the assessment of the degree of septic severity and to aid in the risk stratification of critically ill septic patients. PCT has shown to be useful in decision making to initiate to monitor and stop antibiotic treatment in randomized controlled clinical studies in patients with acute respiratory tract infections and sepsis. PCT is also useful as an antibacterial drug index to prevent severity from lower respiratory tract infection to sepsis.