- Inappropriate use of antibiotics in patients without bacterial infection contributes significantly to worldwide antibiotic resistance.- The goal of this review is to summarise evidence from randomised trials investigating the value of the biomarker procalcitonin (PCT) in patients with symptoms of a bacterial infection in the emergency department (ED) and intensive care (IC).- In patients with a lower respiratory infection in the ED, RCTs demonstrate that withholding or shortening of antibiotic treatment in patients with low PCT levels does not lead to a change in clinical outcome. Similar results were observed in IC patients, where a reduction in PCT level indicates that antibiotics can be discontinued sooner.- In conclusion, initiating and discontinuing antibiotics in ED and IC patients based on PCT levels is safe, appears cost-saving and leads to a reduction in antibiotic use due to fewer antibiotics prescriptions and shortened courses.