Procalcitonin to guide antibiotic therapy in the ICU.

The serum procalcitonin (PCT) concentration reflects both the systemic response to bacterial infection and its severity. However, its accuracy in distinguishing intensive care unit (ICU) patients with and without infection remains low owing to a lack of specificity and the time lapse between infection onset and the PCT rise. Hence, PCT cannot be used as a marker to start or withhold antibiotic therapy for ICU patients. However, the kinetics of the PCT concentration decrease under antibiotic therapy can adequately monitor infection evolution with therapy and can help to customise antibiotic duration. PCT-guided algorithms to guide antibiotic discontinuation were able to shorten antibiotic duration without impacting patient outcomes in several multicentre randomised studies. Notably, antibiotics can be stopped very early when PCT is low and remains low as this indicates that bacterial infection is unlikely. When PCT falls to <0.5 ng/mL or >80% from its peak value, antibiotics for non-localised infections can safely be stopped.