Procalcitonin (PCT) is a peptide measurable in serum which becomes elevated in response to bacterial infection. Multiple trials have explored the safety and efficacy of using PCT as a biomarker to guide decisions about starting or stopping antibiotic therapy in a wide variety of situations, and PCT assays have recently been approved by the Federal Drug Administration (FDA) in the US for use in both sepsis and respiratory tract infections. While there have been a number of promising results particularly in acute respiratory tract infections and intensive care unit settings, problems including adherence to protocol, cost of the assay and improved antimicrobial stewardship more generally, have limited more widespread adoption.This educational article summarises the evidence for the use of procalcitonin as a biomarker of bacterial infection across the spectrum of respiratory disease and reviews how the use of procalcitonin-guided antibiotic therapy is reflected in current major international guidelines.Key pointsProcalcitonin has been widely investigated as a biomarker of bacterial infection to aid diagnosis and decisions to start or stop antibiotics in a range of conditions, including in diseases of the lower respiratory tract.Meta-analysis suggests that the use of procalcitonin to guide antibiotic therapy in acute respiratory tract infections can reduce duration of antibiotic therapy and hospital admission without adversely affecting outcomes – however, there was significant heterogeneity in methodology and population in the included studies, and more recent studies have failed to show such significant benefits.The use of procalcitonin to guide stopping or shortening antibiotic therapy in sepsis/septic shock is suggested in the international guidelines for the management of sepsis (2016), but this is a “weak” recommendation, with a low quality of evidence recognised. Major international guidelines do not support a role for procalcitonin in the management of acute exacerbations of COPD, bronchiectasis, interstitial lung disease or pleural infection.Regardless of situation, decisions on initiating, altering, or discontinuing antimicrobial therapy should never be made solely on the basis of changes in any biomarker – while biomarkers such as procalcitonin may provide supportive information, they should only be used alongside regular and robust clinical assessment.Educational aimsTo understand the principles of using procalcitonin to guide decisions regarding antibiotic use (procalcitonin-guided antibiotic therapy).To review important research studies into the use of procalcitonin as a biomarker of bacterial infection across the spectrum of diseases of the lower respiratory tract.To understand the current international guidelines regarding procalcitonin use in disease of the lower respiratory tract.
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