What is the usefulness of serum procalcitonin (PCT)?

From the Guidelines

Serum procalcitonin (PCT) is a useful biomarker for guiding antibiotic therapy decisions, particularly in respiratory infections and sepsis, and can help reduce unnecessary antibiotic use by identifying patients who don't need antibiotics and by guiding antibiotic discontinuation when levels decrease by 80% from peak or fall below 0.5 ng/mL. The most recent and highest quality study, published in 2023 in the journal Critical Care Medicine 1, suggests that measuring PCT in addition to bedside clinical evaluation can be useful in critically ill patients with a new fever and no clear focus of infection with low to intermediate clinical probability of bacterial infection.

Key Points

• PCT levels below 0.1 ng/mL strongly suggest absence of bacterial infection, while levels above 0.5 ng/mL indicate possible bacterial infection, and values exceeding 2.0 ng/mL strongly suggest sepsis or severe bacterial infection 1.
• Serial measurements of PCT are more informative than single values, with declining levels indicating resolution of infection.
• PCT has advantages over traditional markers like C-reactive protein (CRP) and white blood cell count because it rises more quickly after bacterial infection onset (within 2-4 hours) and has better specificity.
• However, interpretation of PCT requires clinical context, as false positives can occur in conditions like trauma, surgery, and certain cancers, while false negatives may occur in localized infections or if measured too early in the course of infection.

Clinical Application

• Measuring PCT or CRP in critically ill patients with a new fever and no clear focus of infection with low to intermediate clinical probability of bacterial infection is recommended in addition to bedside clinical evaluation, but not in patients with high clinical probability of bacterial infection 1.
• PCT-guided antibiotic treatment in ICU patients with infection and sepsis patients has been shown to result in improved survival and lower antibiotic treatment duration in a meta-analysis of 11 RCTs involving 4,482 patients 1.
• The largest systematic review and meta-analysis to date of 16 studies and greater than 5000 patients showed that PCT-guided antibiotic discontinuation appeared to decrease antibiotic utilization by 1 day and improve mortality, although the evidence was of low certainty 1.

From the Research

Usefulness of Serum Procalcitonin (PCT)

• Serum procalcitonin (PCT) is a host-response biomarker that has shown clinical value for assessing the likelihood of bacterial infections and guiding antibiotic treatment 2.
• PCT can help differentiate bacterial from non-bacterial infections and inflammation states, particularly in respiratory illness 2, 3.
• Several trials have found that PCT-guided antibiotic stewardship reduces antibiotic exposure and associated side-effects among patients with respiratory infection and sepsis 2, 4.

Clinical Applications of PCT

• PCT can be used to guide antibiotic treatment, with low PCT levels helping to rule out bacterial infection in patients with low pretest probability for bacterial infection and low-risk general condition 2.
• In high-risk individuals and/or high pretest probability for infection, empiric antibiotic treatment is mandatory, and subsequent monitoring of PCT can help track the resolution of infection and guide decisions regarding early termination of antibiotic treatment 2, 3.
• PCT may be a reliable marker of infection even in special populations with baseline elevations in serum PCT, but threshold values and clinical criteria should be considered, and antibiotics should never be initiated or withheld based on PCT values alone 3, 4.

Limitations and Future Directions

• The utility of PCT assessment in special patient populations, such as those with renal dysfunction, cardiac compromise, or immunocompromised states, is less clear, and further studies are needed to better understand the application of PCT in these populations 3, 5.
• PCT levels should be considered along with clinical criteria, and the optimal threshold to use in a specific population is unclear 3, 4.
• Further studies are needed to better understand the application of PCT in the diagnosis of sepsis, differentiating between microbial and non-microbial infection cases, and determining the therapeutic approaches for sepsis 6, 5.