Procalcitonin is a peptide precursor of calcitonin that becomes detectable in the setting of systemic bacterial infection, driven by cytokines and endotoxin released throughout the body rather than from the thyroid alone. Levels rise over 12-24 hours with bacterial sepsis and fall as the inflammatory signal resolves. This time course, combined with the sparing in many viral and noninfectious syndromes, makes procalcitonin a useful biomarker conducive to daily trending in the ICU where we constantly balance the risk of missing infection against the harm of prolonged, unnecessary broad-spectrum antibiosis.
Meta-analyses of critically ill adults with sepsis and septic shock show that procalcitonin-guided strategies reliably reduce antibiotic days and increase antibiotic-free days, with outcomes ranging from neutral to modestly improved mortality depending on how the biomarker is used. Importantly, the strongest signal comes from algorithms that primarily use procalcitonin to stop antibiotics rather than to decide when to start them. In a large ICU-specific meta-analysis, only discontinuation strategies clearly reduced both antibiotic exposure and short-term mortality, while mixed or initiation strategies mostly shifted prescribing patterns without changing outcomes.
As a CVICU intensivist, I also have to understand important caveats. Procalcitonin can be elevated in major surgery, trauma, cardiogenic shock, and severe organ dysfunction, and can be blunted early in infection, in very localized processes, or in some immunocompromised states. Some analyses restricted to the sickest septic patients do not show a clear mortality benefit despite shorter courses. To be honest, I don’t find procalcitonin useful in the immediate post-op patients I often take care of because it’s always elevated for noninfectious reasons. For me, it’s important to consider the pre-test probability for an infectious source based on the nature of the pathology/operation, source control issues, etc. Many protocols recommend considering antibiotic discontinuation when procalcitonin falls below an absolute threshold such as 0.5 micrograms/L or drops by at least 80% from its peak, particularly if the patient is hemodynamically stable and source control is addressed.
Here are some PubMed IDs to review the data: 20097417, 26947523, 29168046, 30111341, 24330744
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