What is the clinical significance of Procalcitonin (PCT)?

From the Guidelines

Procalcitonin is a valuable biomarker for guiding antibiotic therapy decisions, particularly in respiratory infections and sepsis, with levels above 0.25-0.5 ng/mL suggesting possible bacterial infection and levels below 0.25 ng/mL or a decrease of 80% from peak indicating discontinuation of antibiotics. When interpreting procalcitonin levels, it's essential to consider the clinical context, as false positives can occur in conditions like trauma, surgery, and certain cancers, while false negatives may happen with localized infections or early-stage infections 1. Some key points to consider when using procalcitonin to guide antibiotic therapy include:

• Normal levels are typically below 0.05 ng/mL, with values above 0.5 ng/mL suggesting possible bacterial infection and levels exceeding 2.0 ng/mL strongly indicating sepsis 1.
• Procalcitonin rises rapidly within 2-4 hours of bacterial infection onset as it's produced by various tissues in response to bacterial toxins and inflammatory cytokines 1.
• Unlike other inflammatory markers like C-reactive protein, procalcitonin is more specific for bacterial infections and isn't significantly elevated in viral infections or non-infectious inflammation 1.
• Serial procalcitonin measurement is recommended in all patients during hospitalization, especially in critically ill or ICU patients, as it may be more predictive of secondary or nosocomial bacterial infection than a single point measurement 1.
• Early de-escalation or discontinuation of antibiotics, within 24 h after admission, in COVID-19 patients with low PCT levels (<0.25 ng/mL) appears to be safe and is associated with a shorter length of hospital stay and potentially lower hospital costs 1.

From the Research

Procalcitonin Overview

• Procalcitonin (PCT) is a prohormone for calcitonin, secreted by the parafollicular cells of the thyroid gland 2
• PCT has been shown to be elevated in bacterial infections but not in viral infections or other inflammatory conditions 2
• The biological activity of PCT is significantly different from calcitonin and is believed to be part of the complex inflammatory cascade of the immune system 2

Clinical Applications of Procalcitonin

• PCT can be used as a biomarker to guide antibiotic therapy, reducing antibiotic exposure and associated side-effects 2, 3
• A cutoff value of 0.25 μg/L in non-ICU patients or 0.5 μg/L in ICU patients seems appropriate for making decisions about the initiation and discontinuation of antibiotic therapy 2
• PCT levels can help differentiate bacterial from non-bacterial infections and inflammation states, particularly in respiratory illness 3
• PCT-guided antibiotic stewardship has been shown to reduce antibiotic exposure and associated side-effects among patients with respiratory infection and sepsis 3

Special Patient Populations

• The utility of PCT assessment in special patient populations, such as those with renal dysfunction, cardiac compromise, or immunocompromised states, is less clear 4
• In special populations, serum PCT may be elevated at baseline and increase further in the presence of infection, requiring higher thresholds for diagnosing infection or de-escalating therapy 4
• PCT-guided antimicrobial therapy may be recommended in certain clinical situations, but PCT levels should be considered along with clinical criteria 4

Pediatric Applications

• PCT can be used to detect invasive infection, differentiate sepsis from noninfectious systemic inflammatory response syndrome, and guide antibiotic therapy in children 5
• Typical values for maximal sensitivity and specificity are less than 0.5 ng/ml for noninfectious inflammation and greater than 2.0 ng/ml for bacterial sepsis 5
• Antibiotic therapy tailored to serial PCT measurements may shorten antibiotic exposure without increasing treatment failure in children 5

Procalcitonin as a Biomarker

• PCT is synthesized by a large number of tissues and organs in response to invasion by pathogenic bacteria, fungi, and some parasites 6
• A growing body of evidence supports the use of PCT as a marker to improve the diagnosis of bacterial infections and guide antibiotic therapy 6
• PCT levels may help guide the need for empirical antibiotic therapy, source control for infections, and duration of antibiotic therapy 6